CABOT MICROELECTRONICS CORPORATION DIRECTORS' DEFERRED COMPENSATION PLAN

Cabot Microelectronics Corporation (the "Company") desires to amend and restate the Directors' Deferred Compensation Plan (the "Plan").  The Plan as originally adopted March 13, 2001 and as amended as of June 17, 2003 (attached hereto as Exhibit A) remains in effect for amounts deferred prior to January 1, 2005.  The Plan was previously amended and restated as of September 26, 2006, and is further amended and restated effective September 23, 2008 as set forth herein.

The Plan is designed to assist the Company in attracting and retaining persons of competence and stature to serve as Directors by giving those Directors the option of deferring receipt of the fees payable to them by the Company for their services as Directors and creating an opportunity for appreciation of fees deferred based on appreciation of the Company's Common Shares.

Therefore, the Company hereby adopts the Plan as hereinafter set forth:

1.   Effective Date .  The Plan is amended and restated effective as of the date executed as set forth below.

2.   Eligibility and Participation .   Each Director of the Company who: (a) is duly elected to the Company's Board of Directors (the "Board of Directors" or the "Board"); (b) receives fees, stipends, awards, or other remuneration ("Directors' Fees") from the Company for services as a Director; and (c) is not an employee of the Company, is an "Eligible Director."  Each Eligible Director may defer receipt of Directors' Fees otherwise payable to that Eligible Director, as provided for in the Plan, beginning on the date he or she is first elected to the Company's Board.  Each Eligible Director who elects to defer Directors' Fees under the Plan is a "Participant" in the Plan.

3.   Administration .   The Board appoints the Company's Chief Executive Officer and the Company's General Counsel to act as the administrators of the Plan (separately and collectively referred to herein as the "Administrator").  The Administrator will serve at the pleasure of the Board of Directors and will administer, construe and interpret the Plan.  The Administrator will not be liable for any act done or determination made in good faith.  The Board of Directors has the power to designate an additional or replacement Administrator at its discretion. The expense of administering the Plan shall be borne by the Company and shall not be charged against benefits payable hereunder.

4.   Deferrals .

(a)   Deferral Election .   An Eligible Director may file with the Administrator, on or before December 31 of each year, an election in writing to defer all or a portion of the Directors' Fees to be earned by the Eligible Director in the following calendar year (a "Deferral Election").  The Deferral Election shall remain in effect until changed or revoked, but as of each December 31 it shall be irrevocable with respect to Directors Fees to be earned by the Director in the immediately following year.   In the year in which a Director first becomes eligible to participate in the Plan, a Deferral Election may be made with respect to services to be performed subsequent to the date of the Deferral Election, if it is filed with the Administrator within thirty (30) days after the date the Director becomes eligible to participate in the Plan.  When a Deferral Election is filed, an amount equal to all or a portion (as designated in the Deferral Election) of the Directors' Fees earned by the Participant for the following calendar year (or the remainder of the calendar year, in the case of new Directors) will be credited to a deferral account maintained on behalf of that Participant (the "Deferral Account").  Each Deferral Election must also specify a distribution commencement date and a method of distribution (lump sum or equal installments), consistent with the terms of paragraph 5.

(b)   Minimum Deferral .  The amount of Deferral Election may not be less than $1,000 per calendar quarter.

(c)   Accounting .  The Deferral Accounts will be maintained by the Company and will list and reflect each Participant's credits and valuations.  The Administrator will provide each Participant an annual statement of the balance in that Participant's Deferral Account.  The Company will credit to each Participant's Deferral Account an amount equivalent to the Directors' Fees or portion thereof, as designated in the Deferral Election, that would have been paid to the Participant if the Participant had not elected to defer such compensation under the Plan.  The credit will be made on the date on which the Directors' Fees would have been paid absent a Deferral Election.  The Plan is unfunded and no funds will be segregated into the Deferral Account of Participants.

(d)   Valuation . Each Deferral Account will be credited a number of Share Units (including fractions thereof) determined by dividing the amount to be credited to the Deferral Account, whether in lieu of payment of Directors' Fees or as a dividend or other distribution attributable to those Share Units, by the Fair Market Value of the Company's Common Shares (as defined below) on the date of credit.  Fair Market Value of the Company's Common Shares means: (i) the closing price of the Company's Common Shares on the principal exchange on which the Company's Common Shares are then trading, if any, on the date such Share Units are to be credited, or, if Shares were not traded on the date of crediting, then on the next preceding trading day during which a sale occurred; or (ii) if the Common Shares are not traded on an exchange but are quoted on the Nasdaq National Market System or a successor quotation system, (1) the last sales price (if the Common Shares are then listed as a National Market Issue under Nasdaq), or (2) the mean between the closing representative bid and asked prices for the Common Shares on the date of credit as reported by Nasdaq or a successor quotation system, or (iii) if the Common Shares are not publicly traded on an exchange and not quoted on Nasdaq or a successor quotation system, the mean between the closing bid and asked prices for the Common Shares on the date of credit, as determined in good faith by the Company's Chief Financial Officer; or (iv) if the Company's Common Shares are not publicly traded, the fair market value established by the Company's Chief Financial Officer acting in good faith.  Each Share Unit will have the value of a Common Share of the Company.  The number of Share Units will be adjusted proportionally to reflect stock splits, stock dividends or other capital adjustments effected without receipt of consideration by the Company, provided, that, in the event of a merger, acquisition or other business combination of the Company with or into another entity, any adjustment provided for in the applicable agreement and plan of merger (or similar document) shall be conclusively deemed to be appropriate for purposes of this Section.

5.   Distribution .   A Participant must elect in writing, at the time each Deferral Election is made under paragraph 4(a), the date on which distribution of the amounts credited to the Participant's Deferral Account to which that Deferral Election relates will commence and the method of distribution, as permitted hereunder.  A Participant's distribution election must specify that distribution will occur on the event or date set forth in paragraph (a)(i) or (ii) below.  The distribution date elected by the Participant for Directors' Fees deferred in a given year shall be the Scheduled Withdrawal Date and may vary with each year, pursuant to the terms of the Deferral Election.  A Participant's Scheduled Withdrawal Date with respect to Directors' Fees deferred in a given year can be no earlier than two years from the last day of the year in which the deferrals are made, other than for "Separation from Service" (as described in paragraph 5(a) below), and will be no later than the date the Participant experiences a Separation from Service as a Director.  Payment will be made in the Company's Common Shares only, in one distribution or equal installment distributions based on the number of Share Units attributable to the applicable Deferral Election.  Installments may not be made more often than monthly and may not extend for more than five years. The time of and method of distribution of benefits may vary with each separate Deferral Election.  The Deferral Accounts represent an unsecured right to acquire the Company's Common Shares.   In the event a Participant does not elect a Scheduled Withdrawal Date, all deferred amounts will be distributed within thirty (30) days following the Participant's Separation from Service (as described in paragraph 5(a) below).

(a)   Time of Distribution .   A Participant's Accounts under the Plan may be paid only upon an event or at a time set forth in this paragraph 5(a):

(i)   The Participant's "Separation from Service" (as defined in Treas. Reg. §1.409A-1(h) and in accordance with Treas. Reg. §1.409A-1(i)(2)).

(ii)   On a s