FLOATING RATE JUNIOR SUBORDINATED DEFERRABLE INTEREST DEBENTURE

Exhibit 4.20

FLOATING RATE JUNIOR SUBORDINATED DEFERRABLE INTEREST DEBENTURE

THIS SECURITY HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “SECURITIES ACT”), ANY STATE SECURITIES LAWS OR ANY OTHER APPLICABLE SECURITIES LAW. NEITHER THIS SECURITY NOR ANY INTEREST OR PARTICIPATION HEREIN MAY BE REOFFERED, SOLD, ASSIGNED, TRANSFERRED, PLEDGED, ENCUMBERED OR OTHERWISE DISPOSED OF IN THE ABSENCE OF SUCH REGISTRATION OR UNLESS SUCH TRANSACTION IS EXEMPT FROM, OR NOT SUBJECT TO, THE REGISTRATION REQUIREMENTS OF THE SECURITIES ACT AND ANY APPLICABLE STATE SECURITIES LAWS. THE HOLDER OF THIS SECURITY BY ITS ACCEPTANCE HEREOF AGREES TO OFFER, SELL OR OTHERWISE TRANSFER THIS SECURITY ONLY (A) TO THE COMPANY, (B) PURSUANT TO A REGISTRATION STATEMENT THAT HAS BEEN DECLARED EFFECTIVE UNDER THE SECURITIES ACT, (C) TO A PERSON WHOM THE SELLER REASONABLY BELIEVES IS A QUALIFIED INSTITUTIONAL BUYER IN A TRANSACTION MEETING THE REQUIREMENTS OF RULE 144A SO LONG AS THIS SECURITY IS ELIGIBLE FOR RESALE PURSUANT TO RULE 144A IN ACCORDANCE WITH RULE 144A, (D) TO A NON-U.S. PERSON IN AN OFFSHORE TRANSACTION IN ACCORDANCE WITH RULE 903 OR RULE 904 (AS APPLICABLE) OF REGULATION S UNDER THE SECURITIES ACT, (E) TO AN INSTITUTIONAL “ACCREDITED INVESTOR” WITHIN THE MEANING OF SUBPARAGRAPH (A) OF RULE 501 UNDER THE SECURITIES ACT THAT IS ACQUIRING THIS SECURITY FOR ITS OWN ACCOUNT, OR FOR THE ACCOUNT OF SUCH AN INSTITUTIONAL ACCREDITED INVESTOR, FOR INVESTMENT PURPOSES AND NOT WITH A VIEW TO, OR FOR OFFER OR SALE IN CONNECTION WITH, ANY DISTRIBUTION IN VIOLATION OF THE SECURITIES ACT, OR (F) PURSUANT TO ANY OTHER AVAILABLE EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF THE SECURITIES ACT, SUBJECT TO THE COMPANY’S RIGHT PRIOR TO ANY SUCH OFFER, SALE OR TRANSFER TO REQUIRE THE DELIVERY OF AN OPINION OF COUNSEL, CERTIFICATION AND/OR OTHER INFORMATION SATISFACTORY TO IT IN ACCORDANCE WITH THE INDENTURE, A COPY OF WHICH MAY BE OBTAINED FROM THE COMPANY.

THE HOLDER OF THIS SECURITY BY ITS ACCEPTANCE HEREOF ALSO AGREES, REPRESENTS AND WARRANTS THAT IT IS NOT AN EMPLOYEE BENEFIT, INDIVIDUAL RETIREMENT ACCOUNT OR OTHER PLAN OR ARRANGEMENT SUBJECT TO TITLE I OF THE EMPLOYMENT RETIREMENT INCOME SECURITY ACT OF 1974, AS AMENDED (“ERISA”), OR SECTION 4975 OF THE INTERNAL REVENUE CODE OF 1986, AS AMENDED (THE “CODE”) (EACH A “PLAN”), OR AN ENTITY WHOSE UNDERLYING ASSETS INCLUDE “PLAN ASSETS” BY REASON OF ANY PLAN’S INVESTMENT IN THE ENTITY, AND NO PERSON INVESTING “PLAN ASSETS” OF ANY PLAN MAY ACQUIRE OR HOLD THE SECURITIES OR ANY INTEREST THEREIN, UNLESS SUCH PURCHASER OR HOLDER IS ELIGIBLE FOR EXEMPTIVE RELIEF AVAILABLE UNDER U.S. DEPARTMENT OF LABOR PROHIBITED TRANSACTION CLASS EXEMPTION 96-23, 95-60, 91-38, 90-1 OR 84-14 OR ANOTHER APPLICABLE EXEMPTION OR ITS PURCHASE AND HOLDING OF THIS SECURITY IS NOT PROHIBITED BY SECTION 406 OF ERISA OR SECTION 4975 OF THE CODE WITH RESPECT TO SUCH PURCHASE OR HOLDING. ANY PURCHASER OR HOLDER OF THE SECURITIES OR ANY INTEREST THEREIN WILL BE DEEMED TO HAVE REPRESENTED BY ITS PURCHASE AND HOLDING THEREOF THAT EITHER (i) IT IS NOT AN EMPLOYEE BENEFIT PLAN WITHIN THE MEANING OF SECTION 3(3) OF ERISA, OR A PLAN TO WHICH SECTION 4975 OF THE CODE IS APPLICABLE, A TRUSTEE OR OTHER PERSON ACTING ON BEHALF OF AN EMPLOYEE BENEFIT PLAN OR PLAN, OR ANY OTHER PERSON OR ENTITY USING THE ASSETS OF ANY EMPLOYEE BENEFIT PLAN OR PLAN TO FINANCE SUCH PURCHASE, OR (ii) SUCH PURCHASE WILL NOT RESULT IN A PROHIBITED TRANSACTION UNDER SECTION 406 OF

ERISA OR SECTION 4975 OF THE CODE FOR WHICH THERE IS NO APPLICABLE STATUTORY OR ADMINISTRATIVE EXEMPTION.

THIS SECURITY WILL BE ISSUED AND MAY BE TRANSFERRED ONLY IN BLOCKS HAVING AN AGGREGATE PRINCIPAL AMOUNT OF NOT LESS THAN $500,000.00 AND MULTIPLES OF $1,000.00 IN EXCESS THEREOF. ANY ATTEMPTED TRANSFER OF THIS SECURITY IN A BLOCK HAVING AN AGGREGATE PRINCIPAL AMOUNT OF LESS THAN $500,000.00 SHALL BE DEEMED TO BE VOID AND OF NO LEGAL EFFECT WHATSOEVER.

THE HOLDER OF THIS SECURITY AGREES THAT IT WILL COMPLY WITH THE FOREGOING RESTRICTIONS.

IN CONNECTION WITH ANY TRANSFER, THE HOLDER WILL DELIVER TO THE REGISTRAR AND TRANSFER AGENT SUCH CERTIFICATES AND OTHER INFORMATION AS MAY BE REQUIRED BY THE INDENTURE TO CONFIRM THAT THE TRANSFER COMPLIES WITH THE FOREGOING RESTRICTIONS.

Floating Rate Junior Subordinated Deferrable Interest Debenture

of

First Financial Bancorp

March 26, 2002

First Financial Bancorp, a California corporation (the “Company” which term includes any successor Person under the Indenture hereinafter referred to), for value received promises to pay to State Street Bank and Trust Company of Connecticut, National Association, not in its individual capacity but solely as Institutional Trustee for First Financial (CA) Statutory Trust I (the “Holder”) or registered assigns, the principal sum of Five Million One Hundred Fifty Five Thousand Dollars ($5,155,000.00) on March 26, 2032, and to pay interest on said principal sum from March 26, 2002, or from the most recent interest payment date (each such date, an “Interest Payment Date”) to which interest has been paid or duly provided for, quarterly (subject to deferral as set forth herein) in arrears on March 26, June 26, September 26 and December 26 of each year commencing June 26, 2002, at an annual rate equal to 5.59% beginning on (and including) the date of original issuance and ending on (but excluding) June 26, 2002 and at an annual rate for each successive period beginning on (and including) June 26, 2002, and each succeeding Interest Payment Date, and ending on (but excluding) the next succeeding Interest Payment Date (each a “Distribution Period”), equal to 3-Month LIBOR, determined as described below, plus 3.60% (the “Coupon Rate”); provided, however, that prior to March 26, 2007, the Coupon Rate shall not exceed 11.00%, applied to the principal amount hereof, until the principal hereof is paid or duly provided for or made available for payment, and on any overdue principal and (without duplication) on any overdue installment of interest at the same rate per annum, compounded quarterly, from the dates such amounts are due until they are paid or made available for payment. The amount of interest payable for any period will be computed on the basis of the actual number of days in the Distribution Period concerned divided by 360. In the event that any date on which interest is payable on this Debenture is not a Business Day, then a payment of the interest payable on such date will be made on the next succeeding day which is a Business Day (and without any interest or other payment in respect of any such delay), except that, if such Business Day is in the next succeeding calendar year, such payment shall be made on the immediately preceding Business Day, in each case with the same force and effect as if made on the date the payment was originally payable. The interest installment so payable, and punctually paid or duly provided for, on any Interest Payment Date will, as provided in the Indenture, be paid to the Person in whose name this Debenture (or one or more Predecessor Securities) is registered at the close of business

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on the regular record date for such interest installment, which shall be fifteen days prior to the day on which the relevant Interest Payment Date occurs. Any such interest installment not so punctually paid or duly provided for shall forthwith cease to be payable to the Holder on such regular record date and may be paid to the Person in whose name this Debenture (or one or more Predecessor Securities) is registered at the close of business on a special record date.

“3-Month LIBOR” as used herein, means the London interbank offered interest rate for three-month U.S. dollar deposits determined by the Trustee in the following order of priority: (i) the rate (expressed as a percentage per annum) for U.S. dollar deposits having a three-month maturity that appears on Telerate Page 3750 as of 11:00 a.m. (London time) on the related Determination Date (“Telerate Page 3750” means the display designated as “Page 3750” on the Dow Jones Telerate Service or such other page as may replace Page 3750 on that service or such other service or services as may be nominated by the British Bankers’ Association as the information vendor for the purpose of displaying London interbank offered rates for U.S. dollar deposits); (ii) if such rate cannot be identified on the related Determination Date, the Trustee will request the principal London offices of four leading banks in the London interbank market to provide such banks’ offered quotations (expressed as percentages per annum) to prime banks in the London interbank market for U.S. dollar deposits having a three-month maturity as of 11:00 a.m. (London time) on such Determination Date. If at least two quotations are provided, 3-Month LIBOR will be the arithmetic mean of such quotations; (iii) if fewer than two such quotations are provided as requested in clause (ii) above, the Trustee will request four major New York City banks to provide such banks’ offered quotations (expressed as percentages per annum) to leading European banks for loans in U.S. dollars as of 11:00 a.m. (London time) on such Determination Date. If at least two such quotations are provided, 3-Month LIBOR will be the arithmetic mean of such quotations; and (iv) if fewer than two such quotations are provided as requested in clause (iii) above, 3-Month LIBOR will be a 3-Month LIBOR determined with respect to the Distribution Period immediately preceding such current Distribution Period. If the rate for U.S. dollar deposits having a three-month maturity that initially appears on Telerate Page 3750 as of 11:00 a.m. (London time) on the related Determination Date is superseded on the Telerate Page 3750 by a corrected rate by 12:00 noon (London time) on such Determination Date, then the corrected rate as so substituted on the applicable page will be the applicable 3-Month LIBOR for such Determination Date. As used herein, “Determination Date” means the date that is two London Banking Days (i.e., a business day in which dealings in deposits in U.S. dollars are transacted in the London interbank market) preceding the commencement of the relevant Distribution Period.

The Coupon Rate for any Distribution Period will at no time be higher than the maximum rate then permitted by New York law as the same may be modified by United States law.

All percentages resulting from any calculations on the Debentures will be rounded, if necessary, to the nearest one hundred-thousandth of a percentage point, with five one-millionths of a percentage point rounded upward (e.g., 9.876545% or .09876545 being rounded to 9.87655% or .0987655, and all dollar amounts used in or resulting from such calculation will be rounded to the nearest cent (with one-half cent being rounded upward)).

The principal of and interest on this Debenture shall be payable at the office or agency of the Trustee (or other paying agent appointed by the Company) maintained for that purpose in any coin or currency of the United States of America that at the time of payment is legal tender for payment of public and private debts; provided, however, that payment of interest may be made by check mailed to the registered holder at such address as shall appear in the Debenture Register if a request for a wire transfer by such holder has not been received by the Company or by wire transfer to an account appropriately designated by the holder hereof. Notwithstanding the foregoing, so long as the holder of this Debenture is

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the Institutional Trustee, the payment of the principal of and interest on this Debenture will be made in immediately available funds at such place and to such account as may be designated by the Trustee.

So long as no Event of Default has occurred and is continuing, the Company shall have the right, from time to time, and without causing an Event of Default, to defer payments of interest on the Debentures by extending the interest payment period on the Debentures at any time and from time to time during the term of the Debentures, for up to 20 consecutive quarterly periods (each such extended interest payment period, an “Extension Period”), during which Extension Period no interest (including Additional Interest) shall be due and payable. No Extension Period may end on a date other than an Interest Payment Date. At the end of any such Extension Period the Company shall pay all interest then accrued and unpaid on the Debentures (together with Additional Interest thereon); provided, however, that no Extension Period may extend beyond the Maturity Date; provided further, however, that during any such Extension Period, the Company shall not and shall not permit any Affiliate to (i) declare or pay any dividends or distributions on, or redeem, purchase, acquire, or make a liquidation payment with respect to, any of the Company’s or such Affiliate’s capital stock (other than payments of dividends or distributions to the Company) or make any guarantee payments with respect to the foregoing or (ii) make any payment of principal of or interest or premium, if any, on or repay, repurchase or redeem any debt securities of the Company or any Affiliate that rank pari passu in all respects with or junior in interest to the Debentures (other than, with respect to clauses (i) and (ii) above, (a) repurchases, redemptions or other acquisitions of shares of capital stock of the Company in connection with any employment contract, benefit plan or other similar arrangement with or for the benefit of one or more employees, officers, directors or consultants, in connection with a dividend reinvestment or stockholder stock purchase plan or in connection with the issuance of capital stock of the Company (or securities convertible into or exercisable for such capital stock) as consideration in an acquisition transaction entered into prior to the applicable Extension Period, (b) as a result of any exchange or conversion of any class or series of the Company’s capital stock (or any capital stock of a subsidiary of the Company) for any class or series of the Company’s capital stock or of any class or series of the Company’s indebtedness for any class or series of the Company’s capital stock, (c) the purchase of fractional interests in shares of the Company’s capital stock pursuant to the conversion or exchange provisions of such capital stock or the security being converted or exchanged, (d) any declaration of a dividend in connection with any stockholders’ rights plan, or the issuance of rights, stock or other property under any stockholders’ rights plan, or the redemption or repurchase of rights pursuant thereto, (e) any dividend in the form of stock, warrants, options or other rights where the dividend stock or the stock issuable upon exercise of such warrants, options or other rights is the same stock as that on which the dividend is being paid or ranks pari passu with or junior to such stock and any cash payments in lieu of fractional shares issued in connection therewith, or (f) payments under the Capital Securities Guarantee). Prior to the termination of any Extension Period, the Company may further extend such period, provided that such period together with all such previous and further consecutive extensions thereof shall not exceed 20 consecutive quarterly periods, or extend beyond the Maturity Date. Upon the termination of any Extension Period and upon the payment of all accrued and unpaid interest and Additional Interest, the Company may commence a new Extension Period, subject to the foregoing requirements. No interest or Additional Interest shall be due and payable during an Extension Period, except at the end thereof, but each installment of interest that would otherwise have been due and payable during such Extension Period shall bear Additional Interest. The Company must give the Trustee notice of its election to begin or extend such Extension Period at least 5 Business Days prior to the earlier of (i) the date interest on the Debentures would have been payable except for the election to begin such Extension Period or (ii) the date such interest is payable, but in any event not less than 5 Business Days prior to such record date.

The indebtedness evidenced by this Debenture is, to the extent provided in the Indenture, subordinate and junior in right of payment to the prior payment in full of all Senior Indebtedness, and this Debenture is issued subject to the provisions of the Indenture with respect thereto. Each holder of this

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Debenture, by accepting the same, (a) agrees to and shall be bound by such provisions, (b) authorizes and directs the Trustee on his or her behalf to take such action as may be necessary or appropriate to acknowledge or effectuate the subordination so provided and (c) appoints the Trustee his or her attorney-in-fact for any and all such purposes. Each holder hereof, by his or her acceptance hereof, hereby waives all notice of the acceptance of the subordination provisions contained herein and in the Indenture by each holder of Senior Indebtedness, whether now outstanding or hereafter incurred, and waives reliance by each such holder upon said provisions.

This Debenture shall not be entitled to any benefit under the Indenture hereinafter referred to, be valid or become obligatory for any purpose until the certificate of authentication hereon shall have been signed by or on behalf of the Trustee.

Capitalized terms used and not defined in this Debenture shall have the meanings assigned in the Indenture dated as of the date of original issuance of this Debenture between the Trustee and the Company.

IN WITNESS WHEREOF, the Company has duly executed this certificate.

CERTIFICATE OF AUTHENTICATION

This is one of the Debentures referred to in the within-mentioned Indenture.

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