RUBICON TECHNOLOGY, INC. AMENDMENT NO. 4 TO THE RUBICONTECHNOLOGY, INC. 2001 EQUITY PLAN DECEMBER 6, 2004

Exhibit 10.1(d)

RUBICON TECHNOLOGY, INC.

AMENDMENT NO. 4

TO THE

RUBICON TECHNOLOGY, INC. 2001 EQUITY PLAN

DECEMBER 6, 2004

This Amendment No. 4 (the “Amendment”) amends the 2001 Equity Plan, dated as of August 2, 2001, as amended by Amendment No. 1, dated as of November 6, 2001, Amendment No. 2, dated as of May 21, 2002 and Amendment No. 3, dated as of My 28, 2004 (the “Plan”) of Rubicon Technology, Inc., a Delaware corporation. Except as expressly modified hereby, all of the terms and provisions of the Plan shall continue in full force and effect.

Subject to the provisions of Section 13 of the Plan and except as provided under Section 3(b) below, the maximum number of Shares which may be optioned or sold under the Plan is Seven Million Six Hundred and Eleven Thousand and One Hundred and Fifty-two (7,611,152) Shares.

(b) Upon the issuance of shares of the Company’s Series C Convertible Preferred Stock, $.001 par value per share after December 8, 2004, the number of Shares reserved under this Section 3 shall automatically be increased to be 12.5% of the fully diluted capital of the Company (assuming the full exercise of any outstanding options, warrants or other rights to purchase Common Stock or any preferred stock of the Company (excluding Options outstanding under this Plan and shares issued as a result of the exercise of Options under this Plan) and the full conversion of any preferred stock of the Company outstanding on that date); provided, however, that in no case shall the number of Shares reserved under the Plan be decreased as a result of the foregoing and no more than twenty percent (20%) of the Shares reserved under the Plan shall be subject, at any one time, to Incentive Stock Options.

This Amendment to the Plan has been adopted by the Board of Directors as of December 6, 2004 and the Stockholders as of December 6, 2004.