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                                                                    Exhibit 10.9


                           EMPLOYEE MATTERS AGREEMENT

                           DATED AS OF MARCH 28, 2000

                                 BY AND BETWEEN

                                CABOT CORPORATION

                                       AND

                       CABOT MICROELECTRONICS CORPORATION
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                           EMPLOYEE MATTERS AGREEMENT

                  This EMPLOYEE MATTERS AGREEMENT, is made as of March 28, 2000
(the "Employee Matters Agreement"), by and between Cabot Corporation ("Cabot")
and Cabot Microelectronics Corporation ("Cabot Microelectronics") (each of Cabot
and Cabot Microelectronics, a "Party," and, collectively, the "Parties").

                                    RECITALS

                  WHEREAS, the Parties have entered into a Master Separation
Agreement ("MSA"), dated as of March 28, 2000, relating to the complete
separation of the "MMD Business" (as defined in the MSA) from Cabot; and

                  WHEREAS, the MSA contemplates that the Parties will enter into
this Employee Matters Agreement to allocate between themselves the
responsibilities, obligations and liabilities relating to the compensation and
employee benefits of the CMC Employees in connection with such separation;

NOW, THEREFORE, in consideration of the covenants and agreements set forth
below, the Parties agree as follows:

         1. DEFINITIONS. As used in this Employee Matters Agreement, the
following terms will have the following meanings, applicable both to the
singular and the plural forms of the terms described:

         (a) "Cabot Qualified Plans" shall mean Cabot's Cash Balance Plan,
Employee Stock Ownership Plan and Retirement Incentive Savings Plan.

         (b) "Cabot Supplemental Plans" shall mean Cabot's Supplemental Cash
Balance Plan, Supplemental Employee Stock Ownership Plan, Supplemental
Retirement Income Savings Plan and Deferred Compensation Plan.

         (c) "CMC Benefit Arrangements" shall mean each and all pension,
supplemental pension, accidental death and dismemberment, life and health
insurance and benefits (including medical, dental, vision, life insurance,
hospitalization, prescription drug, behavioral health and short- and long-term
disability), savings, bonus, deferred compensation, incentive compensation,
holiday, vacation, severance pay, salary continuation, tuition reimbursement,
service award, company car, scholarship, relocation, patent award, fringe
benefit and other employee benefit plans, programs, policies, agreements and
arrangements providing or having any liability to provide compensation or
benefits of any kind to the CMC Employees. The CMC Benefit Arrangements shall
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include, but shall not be limited to, each "employee benefit plan" (as defined
in Section 3(3) of ERISA) of Cabot Microelectronics.

         (d) "CMC Employees" shall mean all persons who are active employees of
Cabot Microelectronics, other than the CMC Foreign Employees. Prior to the
Contribution Date, Cabot Microelectronics and Cabot shall have agreed on the
names of those persons who will be CMC Employees as of the Contribution Date.

         (e) "CMC Foreign Employees" shall mean all persons who are active
employees of Cabot Microelectronics (determined in accordance with the law of
the jurisdictions in which such individuals are located) who reside outside of
the United States.

         (f) "COBRA" shall mean the continuation coverage requirements of
Section 4980B(f) of the Code and Section 601 of ERISA.

         (g) "Code" shall mean the Internal Revenue Code of 1986, as amended.

         (h) "Contribution Date" shall have the meaning set forth in the MSA.

         (i) "Distribution" and "Distribution Date" shall have the meaning set
forth in the MSA.

         (j) "ERISA" shall mean the Employee Retirement Income Security Act of
1974, as amended.

         (k) "IPO Effective Date" shall have the meaning set forth in the MSA.

         (m) "IPO Registration Statement" means the registration statement on
Form S-1, Registration No. 333-90593, filed by Cabot Microelectronics with the
Securities and Exchange Commission in connection with the initial public
offering of the Common Stock, $.001 par value per share, of Cabot
Microelectronics, as it may be amended.

         2. ASSUMPTION BY CABOT MICROELECTRONICS OF RESPONSIBILITIES,
OBLIGATIONS AND LIABILITIES RELATING TO THE CMC EMPLOYEES

         (a) Except as set forth in Section 2(c), as of the Contribution Date,
Cabot Microelectronics shall (or shall cause one or more applicable CMC Benefit
Plans to) assume all responsibilities, obligations and liabilities relating the
employment, compensation and benefits of the CMC Employees as of and following
the Contribution Date. Cabot shall retain all responsibilities, obligations and
liabilities not so assumed by Cabot Microelectronics pursuant to this Employees
Matters Agreement.

         (b) Cabot shall indemnify Cabot Microelectronics and shall hold Cabot
Microelectronics harmless from and against any damages, liabilities, costs or
expenses which may be incurred or suffered by Cabot Microelectronics by reason
of Cabot's failure to comply with any of the provisions of this Employee Matters
Agreement, and Cabot Microelectronics shall indemnify Cabot and its affiliates
(other than Cabot


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Microelectronics) and hold Cabot and its affiliates (other than Cabot
Microelectronics) harmless from and against any damages, liabilities, costs or
expenses which may be incurred or suffered by Cabot and its affiliates (other
than Cabot Microelectronics) by reason of Cabot Microelectronics' failure to
comply with any of the provisions of this Employee Matters Agreement.

         (c) The only exceptions to the responsibilities, obligations and
liabilities assumed by Cabot Microelectronics pursuant to Section 2(a) are as
follows:

                  (i) Cabot shall retain all responsibilities, obligations and
liabilities relating to the Cabot Qualified Plans.

                  (ii) Cabot shall retain all responsibilities, obligations and
liabilities under COBRA and state workers' compensation statutes relating to any
CMC Employee (and, in the case of COBRA benefits, any qualified beneficiary of a
CMC Employee) who becomes entitled to benefits under either of such statutes on
or before the Contribution Date.

                  (iii) Cabot shall retain all responsibilities, obligations and
liabilities for claims arising or incurred on or before the Contribution Date
relating to any CMC Employee under any medical, dental, vision, life insurance,
hospitalization, prescription drug, behavioral health and short-term disability
plan of Cabot. For purposes of this Section 2(c)(iii), a claim shall be deemed
to have arisen or to have been incurred upon the incurrence of a qualified
expense for which reimbursement or payment is sought.

                  (iv) Cabot shall retain all responsibilities, obligations and
liabilities for claims arising or incurred under Cabot's long-term disability
plan with respect to any CMC Employee who becomes entitled to benefits
thereunder on or before the Distribution Date (or such earlier date as Cabot and
Cabot Microelectronics may mutually agree).

                  (v) Stock-based equity awards granted by Cabot to the CMC
Employees pursuant to Cabot's equity incentive plans shall be treated as set
forth in Section 6 of this Employee Matters Agreement. Benefits of the CMC
Employees under the Cabot Supplemental Plans shall be treated as set forth in
Section 7 of this Employee Matters Agreement. Flexible spending accounts of the
CMC Employees under Cabot's flexible benefits plan shall be treated as set forth
in Section 8 of this Employee Matters Agreement.

         (d) Cabot Microelectronics shall promptly reimburse Cabot, upon Cabot's
reasonable request, for any responsibilities, obligations and liabilities
satisfied by Cabot that have been assumed by Cabot Microelectronics pursuant to
this Section 2, and Cabot shall promptly reimburse Cabot Microelectronics, upon
Cabot Microelectronics'


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reasonable request, for any responsibilities, obligations and liabilities
satisfied by Cabot Microelectronics that have been retained by Cabot pursuant to
this Section 2.

         3. ESTABLISHMENT OF CMC BENEFIT ARRANGEMENTS

         (a) Cabot Microelectronics shall establish the following CMC Benefit
Arrangements on or before such times as are set forth below:

                  (i) Qualified Defined Contribution Plan. On or before the IPO
Effective Date, Cabot Microelectronics shall adopt a defined contribution plan
for the benefit of the CMC Employees. Such plan shall be qualified under
Sections 401(a) and 401(k) of the Code and shall contain such rights and
features as Cabot Microelectronics shall determine. The CMC Employees shall
commence to participate in such plan as of the first day of the month
immediately following the month in which the IPO Effective Date occurs.

                  (ii) Employee Stock Purchase Plan. On or before the IPO
Effective Date, Cabot Microelectronics shall adopt an employee stock purchase
plan for the benefit of the CMC Employees. Such plan shall be a plan to which
Section 423 of the Code applies and shall contain such rights and features as
Cabot Microelectronics shall determine. Subject to Section 3(h), the first
offering period under such plan shall commence on the IPO Effective Date (or
such other date as Cabot Microelectronics shall establish).

                  (iii) Supplemental Retirement Plan. On or before the IPO
Effective Date, Cabot Microelectronics shall adopt a supplemental retirement
plan for the purpose of providing supplemental retirement benefits to the CMC
Employees whose contributions to the CMC qualified defined contribution plan are
limited by reason of application of Sections 415(a) and 401(a)(17) of the Code.
Such plan shall in Cabot Microelectronics' discretion be either an "excess
benefit plan" (within the meaning of Section 3(36) of ERISA) or a plan which is
maintained by an employer primarily for the purpose of providing deferred
compensation for a select group of management or highly compensated employees
and shall contain such rights and features as Cabot Microelectronics shall
determine; provided, however, that Cabot Microelectronics shall cause such plan
to be "unfunded" for purposes of ERISA and the Code (but the application of this
proviso shall not preclude Cabot Microelectronics from establishing and making
contributions to one or more grantor trusts relating to such plan). The CMC
Employees shall commence to participate in such plan as of the first day of the
month immediately following the month in which the IPO Effective Date occurs.

                  (iv) Equity Incentive Plan. Prior to the IPO Effective Date,
Cabot Microelectronics shall adopt an equity incentive plan for the purpose of
making equity-based incentive awards relating to the common stock of Cabot
Microelectronics. Subject


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to Section 3(h), equity awards shall be made thereunder as of and after the IPO
Effective Date at such times, in such amounts and to such persons as Cabot
Microelectronics shall determine.

                  (v) Medical and Health Plans. Prior to the Distribution Date,
Cabot Microelectronics shall establish one or more plans providing medical,
dental, vision, life insurance, hospitalization, prescription drug, behavioral
health and short- and long-term disability benefits to the CMC Employees and
their eligible dependents. The CMC Employees shall commence to participate in
such plans as of the Distribution Date (or such earlier date as Cabot and Cabot
Microelectronics may mutually agree).

                  (vi) Employment, Severance and Change-in-Control Agreements
and Arrangements. Following the IPO Effective Date, Cabot Microelectronics shall
enter into such agreements and other arrangements relating to the severance and
termination payments and benefits to which CMC Employees shall become entitled
upon termination of employment following a "change in control" of Cabot
Microelectronics (as defined therein) as Cabot Microelectronics in its sole
discretion deems necessary or advisable. The terms and conditions of these
agreements and arrangements (including, without limitation, eligibility,
conditions to entitlements and nature and amount of payments and benefits) shall
be determined by Cabot Microelectronics in its sole discretion.

         (b) In addition to the CMC Benefit Arrangements to be adopted and
established pursuant to Section 3(a), Cabot Microelectronics shall establish
such other CMC Benefit Arrangements and such other practices and policies
relating thereto as it deems necessary and appropriate for the purpose of
providing compensation and employee benefits to the CMC Employees.

         (c) To the extent that service is relevant to eligibility, vesting or
determination of levels of benefits under any CMC Benefit Arrangement, such CMC
Benefit Arrangement shall provide credit for service by CMC Employees with Cabot
or any of its affiliates (but excluding (i) accrual of benefits under any
defined benefit pension plan that Cabot Microelectronics may establish and (ii)
service awards).

         (d) Cabot Microelectronics shall bear all responsibilities, obligations
and liabilities under the CMC Benefit Arrangements.

         (e) Except as set forth in this Section 3, nothing in this Employee
Matters Agreement shall prohibit Cabot Microelectronics from amending, modifying
or terminating any CMC Benefit Arrangement following the Distribution Date.

         (f) With respect to CMC Benefit Arrangements that provide for medical,
dental, vision, life insurance, hospitalization, prescription drug, behavioral
health and short- and long-term disability benefits or other, similar welfare
benefits, no pre-existing


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conditions exclusions shall be applied to a CMC Employee participating therein
except to the extent such CMC Employee has not satisfied any such exclusion
under the plan of Cabot providing such benefits in which such CMC Employee
participated immediately prior to the commencement of participation in such CMC
Benefit Arrangement. Any amounts for out-of-pocket limits and benefit maximums
paid or incurred in any plan year under any such Cabot plan by a CMC Employee
during such plan year shall be counted toward such CMC Employee's out-of-pocket
limits and benefit maximums under such CMC Benefit Arrangement for the same plan
year.

         (g) The Parties shall take all steps necessary such that (i) any CMC
Benefit Arrangements in effect as of the IPO Effective Date shall comply in form
and in operation with all applicable law (including, without limitation, ERISA,
the Code and the federal securities laws) as of the IPO Effective Date, and (ii)
equity awards granted under the CMC equity incentive plan prior to the
Distribution Date shall constitute qualified performance-based compensation
under Section 162(m) of the Code.

         (h) The Parties shall take all steps necessary such that no issuance of
Cabot Microelectronics common stock shall be made, no Cabot Microelectronics
stock-based equity award shall be granted and no other action shall be taken if
such issuance, grant or other action would preclude the Distribution from being
tax-free to Cabot and its stockholders.

         4. CESSATION OF PARTICIPATION IN CABOT BENEFIT PLANS AND ARRANGEMENTS

         (a) Except as set forth in Sections 4(b), effective as of the IPO
Effective Date, the CMC Employees shall cease to participate in, be covered by,
receive benefits under or have any rights under the employee benefit plans and
arrangements of Cabot, except for benefits and rights relating to their
participation therein prior to the IPO Effective Date.

         (b) The only exceptions to Section 4(a) are as follows:

                  (i) The CMC Employees shall cease to accrue benefits under
Cabot's Cash Balance Plan (and, if applicable, the Cabot Supplemental Plan
relating thereto) on the last day of the month in which the IPO Effective Date
occurs.

                  (ii) The CMC Employees shall receive allocations under Cabot's
Employee Stock Ownership Plan (and, if applicable, the Cabot Supplemental Plan
relating thereto) at the end of the calendar quarter in which the IPO Effective
Date occurs; provided, however, that such allocations shall reflect only service
and compensation through the last day of the month in which the IPO Effective
Date occurs. Cabot shall contribute an amount equal to such contributions to
Cabot's Employee Stock Ownership Plan as soon as practicable following the end
of the calendar quarter in which the IPO


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Effective Date occurs and shall cause such contributions to be allocated to the
accounts of the CMC Employees participating therein.

                  (iii) The CMC Employees shall receive matching contributions
under Cabot's Retirement Incentive Savings Plan (and, if applicable, the Cabot
Supplemental Plan relating thereto) at the end of the calendar quarter in which
the IPO Effective Date occurs; provided, however, that such matching
contributions shall be limited to reflect elective deferrals through the last
day of the month in which the IPO Effective Date occurs. Cabot shall contribute
an amount equal to such contributions to Cabot's Retirement Incentive Savings
Plan as soon as practicable following the end of the calendar quarter in which
the IPO Effective Date occurs and shall cause such contributions to be allocated
to the accounts of the CMC Employees participating therein. Outstanding loans
under Cabot's Retirement Incentive Savings Plan shall be treated as set forth in
Section 5 of this Employee Matters Agreement.

                  (iv) The CMC Employees shall cease to participate in the
medical, dental, vision, life insurance, hospitalization, prescription drug,
behavioral health and short- and long-term disability and other, similar plans
sponsored by Cabot as of the earlier of (x) the date on which they commence to
participate in medical and health plans sponsored by Cabot Microelectronics and
(y) the Distribution Date.

                  (v) The CMC Employees shall cease to participate in Cabot's
Employee Stock Purchase Plan as of the last payroll date prior to the IPO
Effective Date. As soon as practicable following such payroll date, any payroll
deductions of such CMC Employees shall be applied to the purchase of shares of
Cabot common stock, and any excess payroll deductions not so applied shall be
returned to such CMC Employees.

                  (vi) Stock-based equity awards granted by Cabot to the CMC
Employees pursuant to Cabot's equity incentive plans shall be treated as set
forth in Section 6 of this Employee Matters Agreement. Benefits of the CMC
Employees under the Cabot Supplemental Plans shall be treated as set forth in
Section 7 of this Employee Matters Agreement. Flexible spending accounts of the
CMC Employees under Cabot's flexible benefits plan shall be treated as set forth
in Section 8 of this Employee Matters Agreement.

         (c) Prior to the IPO Effective Date, Cabot shall take all action
necessary such that each CMC Employee shall, effective immediately prior to the
Distribution Date, become fully vested in any unvested portion of his or her
accrued benefit under the Cabot Qualified Plans and the Cabot Supplemental
Plans.

         5. TREATMENT OF LOANS UNDER THE CABOT RETIREMENT INCENTIVE SAVINGS
PLAN. Subject to any applicable loan provisions under Cabot's Retirement
Incentive Savings Plan as in effect on the date hereof, Cabot and Cabot


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Microelectronics shall take all actions necessary such that, in connection with
the Distribution, each participant in such plan who is a participant in Cabot
Microelectronics' defined contribution plan is provided with the opportunity to
repay any outstanding loans under the Retirement Incentive Savings Plan and to
establish loans of substantially equal amounts under the Cabot Microelectronics
defined contribution plan.

         6. CONVERSION OF CABOT EQUITY AWARDS. Subject to Section 3(h), equity
awards granted to CMC Employees by Cabot under the equity incentive plans of
Cabot may be converted at such times and in such a manner as Cabot and Cabot
Microelectronics shall agree. As of the date of such conversion, Cabot
Microelectronics shall be deemed to have assumed all such converted awards.

         7. TREATMENT OF LIABILITIES RELATING TO DEFERRED COMPENSATION AND
SUPPLEMENTAL BENEFITS

         (a) Cabot shall take all steps necessary such that: (i) each CMC
Employee who participates in the Cabot Supplemental Plans may elect to reduce to
zero his or her aggregate accrued benefits thereunder and be credited with an
opening account balance of equivalent value under the supplemental retirement
plan established by Cabot Microelectronics pursuant to Section 3(a)(iii) of this
Employee Matters Agreement; and (ii) the aggregate accrued benefits of each CMC
Employee under the Cabot Supplemental Plans who so elects shall, as of the
Distribution Date, be so reduced; provided, however, that no such election by a
CMC Employee so to reduce his or her aggregate accrued benefits under any Cabot
Supplemental Plan shall be of any force and effect unless he or she makes such
election with respect to all of the Cabot Supplemental Plans in which he or she
participates.

         (b) Cabot Microelectronics shall take all steps necessary such that:
(i) the supplemental retirement plan established by it pursuant to Section
3(a)(iii) of this Employee Matters Agreement shall permit the crediting of
opening account balances with respect to each CMC Employee who has made the
election under the Cabot Supplemental Plans contemplated by Section 7(a) of this
Employee Matters Agreement; and (ii) such opening account balance shall, as of
the Distribution Date, be so credited with respect to (and only with respect to)
each CMC Employee who has made such an election.

         (c) Any account balance credited under the Cabot Microelectronics
supplemental retirement plan established by it pursuant to Section 3(a)(iii) of
this Employee Matters Agreement shall be subject to such terms and conditions as
Cabot Microelectronics shall determine; provided, however, that no such term or
condition shall (i) cause any such account balance to be forfeitable and (ii)
without the consent of the applicable CMC Employee, postpone the payment of any
such account balance after termination of his or her employment.


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         (d) As of the Distribution Date, Cabot Microelectronics shall assume
all account balances credited pursuant to this Section 7.

         8. TREATMENT OF FLEXIBLE SPENDING ACCOUNTS.

         (a) Effective as of a date prior to the Distribution Date as the
Parties shall agree, the Parties shall take all steps necessary and appropriate
so that Cabot Microelectronics assumes the Cabot Corporation Flexible Benefits
Plan with respect to the CMC Employees who participate therein (the Cabot
Corporation Flexible Benefits Plan, the "Cabot FBP," and the Cabot
Microelectronics flexible benefits plan resulting from such assumption, the "CMC
FBP"). To the extent that the date of such assumption is other than as of the
first day of a plan year of the Cabot FBP (such date of assumption, the
"Assumption Date"): (x) the Parties shall take all steps necessary or
appropriate so that the book entry account balances (reflecting salary
deductions, deemed employer contributions (if any) and qualified expenses paid
(if any)) under the Cabot FBP of each such CMC Employee shall become account
balances, as of the Assumption Date, under the CMC FBP; and (y) the Parties
shall take all steps necessary or appropriate so that the contribution elections
of each such CMC Employee as in effect immediately before the Assumption Date
under the Cabot FBP remain in effect under the CMC FBP immediately after the
Assumption Date.

         (b) As soon as practicable following March 31 following the plan year
of the Cabot FBP in which the Assumption Date occurs, Cabot and Cabot
Microelectronics shall agree upon the appropriate method of allocating between
them any losses suffered by either of them by reason of Section 8(a) of this
Employee Matters Agreement.

         9. FOREIGN EMPLOYEES. As of the Contribution Date, Cabot
Microelectronics shall assume all responsibilities, obligations and liabilities
relating to the employment, compensation and benefits of the CMC Foreign
Employees as of and following the Contribution Date. Cabot shall retain all
responsibilities, obligations and liabilities not so assumed by Cabot
Microelectronics pursuant to this Section 9.

         10. COOPERATION.

         (a) Cabot Microelectronics and Cabot shall reasonably cooperate with
each other in carrying out the terms of this Employee Matters Agreement with the
purpose of effectuating the intent hereof, and each Party shall exchange such
information with the other Party as may be reasonably requested by the other
Party relating hereto.

         (b) Each of the Parties shall provide to the other Party, upon such
other Party's reasonable request, any and all information in such Party's
possession which relates to such Party's employee benefit plans, programs and
arrangements, including, without limitation, annual reports on Form 5500,
actuarial valuations and materials relating to


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nondiscrimination and coverage; provided, however, that (i) no Party shall be
required (x) to prepare any document in response to any such request or (y) to
produce any document which is subject to a claim of privilege, and (ii) no Party
shall be required to respond to any such request to the extent that such request
relates to any period other than the period commencing on January 1, 1999 and
ending, with respect to all of the Parties' employee benefit plans, programs and
arrangements other than the Parties' tax-qualified plans, on the third
anniversary of the Distribution Date, and ending, with respect to the Parties'
tax-qualified plans, on December 31 of the year in which the sixth anniversary
of the Distribution Date occurs.

         11. ORDER OF PRECEDENCE. The Parties agree that, if any terms of this
Employee Matters Agreement conflict with the terms in the MSA, the terms of this
Employee Matters Agreement shall govern with respect to the resolution of such
conflict.

         12. INCORPORATION OF ARTICLE 7 OF THE MSA. The provisions of Article 7
of the MSA are incorporated into and made part of this Employee Matters
Agreement by reference.

         13. EFFECTIVE TIME. This Agreement shall become effective upon the
closing of the initial public offering described in the IPO Registration
Statement.

IN WITNESS WHEREOF, the Parties hereto have executed this Employee Matters
Agreement, effective as of the date first written above.

                                       CABOT MICROELECTRONICS
CABOT CORPORATION                      CORPORATION




/s/ Samuel W. Bodman                   /s/ Matthew Neville
---------------------------------      -------------------------------------
By:  Samuel W. Bodman                  By:  Matthew Neville
Its:  Chairman and CEO                 Its:  President and CEO


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