Amendment to Non-Qualified Stock Option Grant Agreements between Cabot Microelectronics Corporation and Juan Enriquez Cabot (Dated January 29, 2005)

AMENDMENT AS OF JANUARY 29, 2005

TO THREE GRANT AGREEMENTS FOR NON-QUALIFIED STOCK OPTION AWARDS WITH GRANT DATES OF MARCH 13, 2001, MARCH 12, 2002 AND MARCH 11, 2003, RESPECTIVELY (“AMENDMENT”)

WHEREAS, Juan Enriquez Cabot (“you”) and Cabot Microelectronics Corporation (the “Company”) desire to amend the Grant Agreements setting forth the terms under which, pursuant to the Second Amended and Restated Cabot Microelectronics Corporation 2000 Equity Incentive Plan and predecessor plans (the “Plan”), you received one non-qualified stock option Award (Grant #619) with a Grant Date of March 13, 2001 (“2001 Grant Agreement”), one non-qualified stock option Award (Grant #1,159) with a Grant Date of March 12, 2002 (“2002 Grant Agreement”), and one non-qualified stock option Award (Grant #1801) with a Grant Date of March 11, 2003 (“2003 Grant Agreement”), as contemplated by the Board of Directors of the Company;

NOW, THEREFORE, you and the Company agree that the 2001 Grant Agreement is hereby amended effective as of January 29, 2005, as follows:

In the prefatory paragraph in the box entitled “Vesting Dates”, in the fourth line the clause “3/13/05” is hereby removed and replaced with “3/10/05, assuming your resignation as a director”; and,

In the section entitled, “1. Vesting and Exercise.”, in the fourth line of “Installment”, and second column of “Vesting Date Applicable to Installment”, the clause “March 13, 2005” is hereby removed and replaced with “March 10, 2005, assuming your resignation as a director”.

AGREED FURTHER, that the 2002 Grant Agreement is hereby amended effective as of January 29, 2005, as follows:

In the prefatory paragraph in the box entitled “Vesting Dates”, in the third line the clause “3/12/05” is hereby removed and replaced with “3/10/05, assuming your resignation as a director”; and,

In the section entitled, “1. Vesting and Exercise.”, in the third line of “Installment”, and second column of “Vesting Date Applicable to Installment”, the clause “March 12, 2005” is hereby removed and replaced with “March 10, 2005, assuming your resignation as a director”.

AGREED FURTHER, that the 2003 Grant Agreement is hereby amended effective as of January 29, 2005, as follows:

In the prefatory paragraph in the box entitled “Vesting Dates”, in the second line the clause “3/11/2005” is hereby removed and replaced with “3/10/2005, assuming your resignation as a director”; and,

In the section entitled, “1. Vesting and Exercise.”, in the second line of “Installment”, and second column of “Vesting Date Applicable to Installment”, the clause “March 11, 2005” is hereby removed and replaced with “March 10, 2005, assuming your resignation as a director”.

All other terms of each of the 2001, 2002 and 2003 Grant Agreements remain unchanged and unaffected by this Amendment.