Spirit of Texas Bancshares, Inc. 2008 Stock Plan

Exhibit 10.5

ST FINANCIAL GROUP, INC.

2008 STOCK PLAN

ST FINANCIAL GROUP, INC. 2008 STOCK PLAN

SECTION 1. ESTABLISHMENT AND PURPOSE.

The purpose of the Plan is to offer selected persons an opportunity to acquire a proprietary interest in the success of the Company, or to increase such interest, by purchasing Shares of the Company’s Stock. The Plan provides both for the direct award or sale of Shares and for the grant of Options to purchase Shares. Options granted under the Plan may include Nonstatutory Options as well as ISOs intended to qualify under Section 422 of the Code.

Capitalized terms are defined in Section 12.

SECTION 2. ADMINISTRATION.

(a) Committees of the Board of Directors. The Plan may be administered by one or more Committees. Each Committee shall consist of one or more members of the Board of Directors who have been appointed by the Board of Directors. Each Committee shall have such authority and be responsible for such functions as the Board of Directors has assigned to it. If no Committee has been appointed, the entire Board of Directors shall administer the Plan. Any reference to the Board of Directors in the Plan shall be construed as a reference to the Committee (if any) to whom the Board of Directors has assigned a particular function.

(b) Authority of the Board of Directors. Subject to the provisions of the Plan, the Board of Directors shall have full authority and discretion to take any actions it deems necessary or advisable for the administration of the Plan. All decisions, interpretations and other actions of the Board of Directors shall be final and binding on all Purchasers, all Optionees and all persons deriving their rights from a Purchaser or Optionee.

SECTION 3. ELIGIBILITY.

(a) General Rule. Only Employees, Outside Directors and Consultants shall be eligible for the grant of Nonstatutory Options or the direct award or sale of Shares. Only Employees shall be eligible for the grant of ISOs.

(b) Ten-Percent Stockholders. A person who owns more than 10% of the total combined voting power of all classes of outstanding stock of the Company, its Parent or any of its Subsidiaries shall not be eligible for the grant of an ISO unless (i) the Exercise Price is at least 110% of the Fair Market Value of a Share on the date of grant and (ii) such ISO by its terms is not exercisable after the expiration of five years from the date of grant. For purposes of this Subsection (b), in determining stock ownership, the attribution rules of Section 424(d) of the Code shall be applied.

1

SECTION 4. STOCK SUBJECT TO PLAN.

(a) Basic Limitation. Not more than [20% OF THE NUMBER OF SHARES SOLD IN THE OFFERING] Shares may be issued under the Plan (subject to Subsection (b) below and Section 8). The number of Shares that are subject to Options or other rights outstanding at any time under the Plan shall not exceed the number of Shares that then remain available for issuance under the Plan. The Company, during the term of the Plan, shall at all times reserve and keep available sufficient Shares to satisfy the requirements of the Plan. Shares offered under the Plan may be authorized but unissued Shares or treasury Shares.

(b) Additional Shares. In the event that Shares previously issued under the Plan are reacquired by the Company pursuant to a forfeiture provision, right of repurchase or right of first refusal, such Shares shall be added to the number of Shares then available for issuance under the Plan. However, the aggregate number of Shares issued upon the exercise of ISOs (including Shares reacquired by the Company) shall in no event exceed 200% of the number specified in Subsection (a) above. In the event that an outstanding Option or other right for any reason expires or is canceled, the Shares allocable to the unexercised portion of such Option or other right shall not reduce the number of Shares available for issuance under the Plan.

SECTION 5. TERMS AND CONDITIONS OF AWARDS OR SALES.

(a) Stock Purchase Agreement. Each award or sale of Shares under the Plan (other than upon exercise of an Option) shall be evidenced by a Stock Purchase Agreement between the Purchaser and the Company. Such award or sale shall be subject to all applicable terms and conditions of the Plan and may be subject to any other terms and conditions which are not inconsistent with the Plan and which the Board of Directors deems appropriate for inclusion in a Stock Purchase Agreement. The provisions of the various Stock Purchase Agreements entered into under the Plan need not be identical.

(b) Duration of Offers and Nontransferability of Rights. Any right to acquire Shares under the Plan (other than an Option) shall automatically expire if not exercised by the Purchaser within 30 days after the grant of such right was communicated to the Purchaser by the Company. In addition, if the Company’s capital falls below the minimum regulatory requirements, the Company, if directed by its federal or state regulators, may require the Purchaser to exercise or forfeit such right within such shorter period of time as is required by such regulators. Such right shall not be transferable and shall be exercisable only by the Purchaser to whom such right was granted.

(c) Purchase Price. The Purchase Price of Shares to be offered under the Plan, if newly issued, shall not be less than the Fair Market Value of such Shares. Subject to the preceding sentence, the Board of Directors shall determine the Purchase Price at its sole discretion. The Purchase Price shall be payable in a form described in Section 7.

(d) Withholding Taxes. As a condition to the purchase of Shares, the Purchaser shall make such arrangements as the Board of Directors may require for the satisfaction of any federal, state, local or foreign withholding tax obligations that may arise in connection with such purchase.

2

(e) Restrictions on Transfer of Shares. Any Shares awarded or sold under the Plan shall be subject to such special forfeiture conditions, rights of repurchase, rights of first refusal and other transfer restrictions as the Board of Directors may determine. Such restrictions shall be set forth in the applicable Stock Purchase Agreement and shall apply in addition to any restrictions that may apply to holders of Shares generally. A Stock Purchase Agreement may provide for accelerated vesting in the event of the Purchaser’s death, disability or retirement or other events.

SECTION 6. TERMS AND CONDITIONS OF OPTIONS.

(a) Stock Option Agreement. Each grant of an Option under the Plan shall be evidenced by a Stock Option Agreement between the Optionee and the Company. Such Option shall be subject to all applicable terms and conditions of the Plan and may be subject to any other terms and conditions which are not inconsistent with the Plan and which the Board of Directors deems appropriate for inclusion in a Stock Option Agreement. The provisions of the various Stock Option Agreements entered into under the Plan need not be identical.

(b) Number of Shares. Each Stock Option Agreement shall specify the number of Shares that are subject to the Option and shall provide for the adjustment of such number in accordance with Section 8. The Stock Option Agreement shall also specify whether the Option is an ISO or a Nonstatutory Option.

(c) Exercise Price. Each Stock Option Agreement shall specify the Exercise Price. The Exercise Price of an ISO shall not be less than 100% of the Fair Market Value of a Share on the date of grant, and a higher percentage may be required by Section 3(b). The Exercise Price of a Nonstatutory Option to purchase newly issued Shares shall not be less than 100% of the Fair Market Value of a Share on the date of grant. Subject to the preceding two sentences, the Exercise Price under an Option shall be determined by the Board of Directors at its sole discretion. The Exercise Price shall be payable in a form described in Section 7.

(d) Exercisability. Each Stock Option Agreement shall specify the date when all or any installment of the Option is to become exercisable. No Option shall be exercisable unless the Optionee has delivered an executed copy of the Stock Option Agreement to the Company. The Board of Directors shall determine the exercisability provisions of any Stock Option Agreement at its sole discretion.

(e) Accelerated Exercisability. Unless the applicable Stock Option Agreement provides otherwise, all of an Optionee’s Options shall become exercisable in full if (i) the Company is subject to a Change in Control before the Optionee’s Service terminates, (ii) such Options do not remain outstanding, (iii) such Options are not assumed by the surviving corporation or its parent and (iv) the surviving corporation or its parent does not substitute options with substantially the same terms for such Options. A Stock Option Agreement may also provide for accelerated exercisability in the event of the Optionee’s death, disability or retirement or other events.

3

(f) Term. The Stock Option Agreement shall specify the term of the Option. The term shall not exceed 10 years from the date of grant, and in the case of an ISO a shorter term may be required by Section 3(b). Subject to the preceding sentence, the Board of Directors at its sole discretion shall determine when an Option is to expire. A Stock Option Agreement may provide for expiration prior to the end of its term in the event of the termination of the Optionee’s Service or death. In addition, if the Company’s capital falls below the minimum regulatory requirements, the Company, if directed by its federal or state regulators, may require the Option holder to exercise or forfeit that portion of its Option that is capable of exercise and to forfeit that portion of its Option that is not capable of exercise within such shorter period of time as is required by such regulators.

(g) Restrictions on Transfer of Shares. Any Shares issued upon exercise of an Option shall be subject to such special forfeiture conditions, rights of repurchase, rights of first refusal and other transfer restrictions as the Board of Directors may determine. Such restrictions shall be set forth in the applicable Stock Option Agreement and shall apply in addition to any restrictions that may apply to holders of Shares generally.

(h) Transferability of Options. An Option shall be transferable by the Optionee only by (i) a beneficiary designation, (ii) a will or (iii) the laws of descent and distribution, except as provided in the next sentence. If the applicable Stock Option Agreement so provides, a Nonstatutory Option shall also be transferable by the Optionee by (i) a gift to a member of the Optionee’s Immediate Family or (ii) a gift to an inter vivos or testamentary trust in which members of the Optionee’s Immediate Family have a beneficial interest of more than 50% and which provides that such Nonstatutory Option is to be transferred to the beneficiaries upon the Optionee’s death. An ISO may be exercised during the lifetime of the Optionee only by the Optionee or by the Optionee’s guardian or legal representative.

(i) Withholding Taxes. As a condition to the exercise of an Option, the Optionee shall make such arrangements as the Board of Directors may require for the satisfaction of any federal, state, local or foreign withholding tax obligations that may arise in connection with such exercise. The Optionee shall also make such arrangements as the Board of Directors may require for the satisfaction of any federal, state, local or foreign withholding tax obligations that may arise in connection with the disposition of Shares acquired by exercising an Option.

(j) No Rights as a Stockholder. An Optionee, or a transferee of an Optionee, shall have no rights as a stockholder with respect to any Shares covered by the Optionee’s Option until such person becomes entitled to receive such Shares by filing a notice of exercise and paying the Exercise Price pursuant to the terms of such Option.

(k) Modification, Extension and Assumption of Options. Within the limitations of the Plan, the Board of Directors may modify, extend or assume outstanding Options or may accept the cancellation of outstanding Options (whether granted by the Company or another issuer) in return for the grant of new Options for the same or a different number of Shares and at the same or a different Exercise Price. The foregoing notwithstanding, no modification of an Option shall, without the consent of the Optionee, impair the Optionee’s rights or increase the Optionee’s obligations under such Option.

4

SECTION 7. PAYMENT FOR SHARES.

(a) General Rule. The entire Purchase Price or Exercise Price of Shares issued under the Plan shall be payable in cash or cash equivalents at the time when such Shares are purchased, except as otherwise provided in this Section 7.

(b) Surrender of Stock. To the extent that a Stock Option Agreement so provides, all or any part of the Exercise Price may be paid by surrendering, or attesting to the ownership of, Shares that are already owned by the Optionee. Such Shares shall be surrendered to the Company in good form for transfer and shall be valued at their Fair Market Value on the date when the Option is exercised. The Optionee shall not surrender, or attest to the ownership of, Shares in payment of the Exercise Price if such action would cause the Company to recognize compensation expense (or additional compensation expense) with respect to the Option for financial reporting purposes.

(c) Services Rendered. At the discretion of the Board of Directors, Shares may be awarded under the Plan in consideration of services rendered to the Company, a Parent or a Subsidiary prior to the award.

(d) Promissory Note. To the extent that a Stock Option Agreement or Stock Purchase Agreement so provides, all or a portion of the Exercise Price or Purchase Price (as the case may be) of Shares issued under the Plan may be paid with a full-recourse promissory note. However, the par value of the Shares, if newly issued, shall be paid in cash or cash equivalents. The Shares shall be pledged as security for payment of the principal amount of the promissory note and interest thereon. The interest rate payable under the terms of the promissory note shall not be less than the minimum rate (if any) required to avoid the imputation of additional interest under the Code. Subject to the foregoing, the Board of Directors (at its sole discretion) shall specify the term, interest rate, amortization requirements (if any) and other provisions of such note.

(e) Exercise/Sale. To the extent that a Stock Option Agreement so provides, and if Stock is publicly traded, payment may be made all or in part by the delivery (on a form prescribed by the Company) of an irrevocable direction to a securities broker approved by the Company to sell Shares and to deliver all or part of the sales proceeds to the Company in payment of all or part of the Exercise Price and any withholding taxes.

(f) Exercise/Pledge. To the extent that a Stock Option Agreement so provides, and if Stock is publicly traded, payment may be made all or in part by the delivery (on a form prescribed by the Company) of an irrevocable direction to pledge Shares to a securities broker or lender approved by the Company, as security for a loan, and to deliver all or part of the loan proceeds to the Company in payment of all or part of the Exercise Price and any withholding taxes.

5

SECTION 8. ADJUSTMENT OF SHARES.

(a) General. In the event of a subdivision of the outstanding Stock, a declaration of a dividend payable in Shares, a declaration of an extraordinary dividend payable in a form other than Shares in an amount that has a material effect on the Fair Market Value of the Stock, a combination or consolidation of the outstanding Stock into a lesser number of Shares, a recapitalization, a spin-off, a reclassification or a similar occurrence, the Board of Directors shall make appropriate adjustments in one or more of (i) the number of Shares available for future grants under Section 4, (ii) the number of Shares covered by each outstanding Option or (iii) the Exercise Price under each outstanding Option.

(b) Mergers and Consolidations. In the event that the Company is a party to a merger or consolidation, outstanding Options shall be subject to the agreement of merger or consolidation. Such agreement shall provide for:

(i) The continuation of such outstanding Options by the Company (if the Company is the surviving corporation);

(ii) The assumption of the Plan and such outstanding Options by the surviving corporation or its parent;

(iii) The substitution by the surviving corporation or its parent of options with substantially the same terms for such outstanding Options;

(iv) The full exercisability of such outstanding Options and full vesting of the Shares subject to such Options, followed by the cancellation of such Options; or

(v) The settlement of the full value of such outstanding Options (whether or not then exercisable) in cash or cash equivalents, followed by the cancellation of such Options.

(c) Reservation of Rights. Except as provided in this Section 8, an Optionee or Purchaser shall have no rights by reason of (i) any subdivision or consolidation of shares of stock of any class, (ii) the payment of any dividend or (iii) any other increase or decrease in the number of shares of stock of any class. Any issuance by the Company of shares of stock of any class, or securities convertible into shares of stock of any class, shall not affect, and no adjustment by reason thereof shall be made with respect to, the number or Exercise Price of Shares subject to an Option. The grant of an Option pursuant to the Plan shall not affect in any way the right or power of the Company to make adjustments, reclassifications, reorganizations or changes of its capital or business structure, to merge or consolidate or to dissolve, liquidate, sell or transfer all or any part of its business or assets.

SECTION 9. SECURITIES LAW REQUIREMENTS.

Shares shall not be issued under the Plan unless the issuance and delivery of such Shares comply with (or are exempt from) all applicable requirements of law, including (without limitation) the Securities Act of 1933, as amended, the rules and regulations promulgated thereunder, state securities laws and regulations, and the regulations of any stock exchange or other securities market on which the Company’s securities may then be traded.

6

(n) “Optionee” shall mean a person who holds an Option.

(o) “Outside Director” shall mean a member of the Board of Directors who is not an Employee.

(p) “Parent” shall mean any corporation (other than the Company) in an unbroken chain of corporations ending with the Company, if each of the corporations other than the Company owns stock possessing 50% or more of the total combined voting power of all classes of stock in one of the other corporations in such chain. A corporation that attains the status of a Parent on a date after the adoption of the Plan shall be considered a Parent commencing as of such date.

(q) “Plan” shall mean this ST Financial Group, Inc. 2008 Stock Plan.

(r) “Purchase Price” shall mean the consideration for which one Share may be acquired under the Plan (other than upon exercise of an Option), as specified by the Board of Directors.

(s) “Purchaser” shall mean a person to whom the Board of Directors has offered the right to acquire Shares under the Plan (other than upon exercise of an Option).

(t) “Service” shall mean service as an Employee, Outside Director or Consultant.

(u) “Share” shall mean one share of Stock, as adjusted in accordance with Section 8 (if applicable).

(v) “Stock” shall mean the Common Stock of the Company, with a par value of $5.00 per Share.

(w) “Stock Option Agreement” shall mean the agreement between the Company and an Optionee that contains the terms, conditions and restrictions pertaining to the Optionee’s Option.

(x) “Stock Purchase Agreement” shall mean the agreement between the Company and a Purchaser who acquires Shares under the Plan that contains the terms, conditions and restrictions pertaining to the acquisition of such Shares.

(y) “Subsidiary” shall mean any corporation (other than the Company) in an unbroken chain of corporations beginning with the Company, if each of the corporations other than the last corporation in the unbroken chain owns stock possessing 50% or more of the total combined voting power of all classes of stock in one of the other corporations in such chain. A corporation that attains the status of a Subsidiary on a date after the adoption of the Plan shall be considered a Subsidiary commencing as of such date.

9