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                                                                    EXHIBIT 10.2

                              MKS INSTRUMENTS, INC.

                THIRD RESTATED 1999 EMPLOYEE STOCK PURCHASE PLAN
                              (AS OF MAY 13, 2004)

      The purpose of this Plan is to provide eligible employees of MKS
Instruments, Inc. (the "Company") and certain of its subsidiaries with
opportunities to purchase shares of the Company's Common Stock, no par value per
share (the "Common Stock"), commencing on June 1, 1999; provided, that at such
time the Company's Common Stock shall be listed for trading on the Nasdaq
National Market or a national securities exchange. An aggregate of 1,250,000
shares of Common Stock have been approved for this purpose. This Plan is
intended to qualify as an "employee stock purchase plan" as defined in Section
423 of the Internal Revenue Code of 1986, as amended (the "Code") and the
regulations promulgated thereunder, and shall be interpreted consistent
therewith.

1. Administration. The Plan will be administered by the Company's Board of
Directors (the "Board") or by a Committee appointed by the Board (the
"Committee"). The Board or the Committee has authority to make rules and
regulations for the administration of the Plan and its interpretation and
decisions with regard thereto shall be final and conclusive.

2. Eligibility. All employees of the Company, including Directors who are
employees, and all employees of any subsidiary of the Company (as defined in
Section 424(f) of the Code) designated by the Board or the Committee from time
to time (a "Designated Subsidiary"), including employees of the Company or any
designated Subsidiary who are "highly compensated" within the meaning of Section
414(q) of the Code, are eligible to participate in any one or more of the
Offerings (as defined in Section 9) to purchase Common Stock under the Plan
provided that:

            (a) they are customarily employed by the Company or a Designated
      Subsidiary for more than 20 hours a week and for more than five months in
      a calendar year; and

            (b) they have been employed by the Company or a Designated
      Subsidiary for at least three (3) months prior to enrolling in the Plan;
      and

            (c) they are employees of the Company or a Designated Subsidiary on
      the first day of the applicable Plan Period (as defined below).

      No employee may be granted an option hereunder if such employee,
immediately after the option is granted, owns 5% or more of the total combined
voting power or value of the stock of the Company or any subsidiary. For
purposes of the preceding sentence, the attribution rules of Section 424(d) of
the Code shall apply in determining the stock ownership of an employee, and all
stock which the employee has a contractual right to purchase shall be treated as
stock owned by the employee.
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3. Offerings. The Company will make one or more offerings ("Offerings") to
employees to purchase stock under this Plan. Offerings will begin each June 1
and December 1, or the first business day thereafter (the "Offering Commencement
Dates"). Each Offering Commencement Date will begin a six (6) month period (a
"Plan Period") during which Payroll deductions will be made and held for the
purchase of Common Stock at the end of the Plan Period. The Board or the
Committee may, at its discretion, choose a different Plan Period of twelve (12)
months or less for subsequent Offerings.

4. Participation. An employee eligible on the Offering Commencement Date of any
Offering may participate in such Offering by completing and forwarding a payroll
deduction authorization form to the employee's appropriate payroll office at
least 30 days prior to the applicable Offering Commencement Date. The form will
authorize a regular payroll deduction from the Compensation, as defined below,
received by the employee during the Plan Period. Unless an employee files a new
form or withdraws from the Plan, his deductions and purchases will continue at
the same rate for future Offerings under the Plan as long as the Plan remains in
effect. The term "Compensation" means the amount of money reportable on the
employee's Federal Income Tax Withholding Statement, including overtime, shift
premium, incentive or bonus awards and any other variable sales compensation and
excluding allowances and reimbursements for expenses such as relocation
allowances for travel expenses, income or gains on the exercise of Company stock
options or stock appreciation rights, and similar items, whether or not shown on
the employee's Federal Income Tax Withholding Statement, but including, in the
case of salespersons, sales commissions to the extent determined by the Board or
the Committee.

5. Deductions. The Company will maintain payroll deduction accounts for all
participating employees. With respect to any Offering made under this Plan, an
employee may authorize a payroll deduction in any whole percent amount up to a
maximum of 10% (or such lower percentage as may be established by the Board or
the Committee) of the Compensation he or she receives during the Plan Period or
such shorter period during which deductions from payroll are made. The minimum
payroll deduction is such percentage of compensation as may be established from
time to time by the Board or the Committee.

      No employee may be granted an Option (as defined in Section 9) which
permits his rights to purchase Common Stock under this Plan and any other
employee stock purchase plan (as defined in Section 423(b) of the Code) of the
Company and its subsidiaries, to accrue at a rate which exceeds $25,000 of the
fair market value of such Common Stock (determined at the Offering Commencement
Date of the Plan Period) for each calendar year in which the Option is
outstanding at any time.

6. Deduction Changes. An employee may decrease, subject to section 5 hereof or
discontinue his payroll deduction once during any Plan Period, by filing a new
payroll deduction authorization form. However, an employee may not elect to
increase his payroll deduction during


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a Plan Period. If an employee elects to discontinue his payroll deductions
during a Plan Period, but does not elect to withdraw his funds pursuant to
Section 8 hereof, funds deducted prior to his election to discontinue will be
applied to the purchase of Common Stock on the Exercise Date (as defined below).

7. Interest. Interest will not be paid on employee accounts.

8. Withdrawal of Funds. An employee may at any time prior to the close of
business on the last business day in a Plan Period and for any reason
permanently draw out the balance accumulated in the employee's account and
thereby withdraw from participation in an Offering. Partial withdrawals are not
permitted. The employee may not begin participation again during the remainder
of the Plan Period. The employee may participate in any subsequent Offering in
accordance with terms and conditions established by the Board or the Committee.

9. Purchase of Shares. On the Offering Commencement Date of each Plan Period,
the Company will grant to each eligible employee who is then a participant in
the Plan an option ("Option") to purchase on the last business day of such Plan
Period (the "Exercise Date"), at the Option Price hereinafter provided for, the
largest number of shares (fractional or whole) of Common Stock of the Company as
does not exceed the number of shares determined by multiplying $2,083 by the
number of full months in the Offering Period and dividing the results by the
closing price (as defined below) on the Offering Commencement Date of such Plan
Period.


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      The purchase price for each share purchased will be 85% of the closing
price of the Common Stock on (i) the first business day of such Plan Period or
(ii) the Exercise Date, whichever closing price shall be less. Such closing
price shall be (a) the closing price on any national securities exchange on
which the Common Stock is listed, (b) the closing price of the Common Stock on
the Nasdaq National Market or (c) the average of the closing bid and asked
prices in the over-the-counter-market, whichever is applicable, as published in
The Wall Street Journal. If no sales of Common Stock were made on such a day,
the price of the Common Stock for purposes of clauses (a) and (b) above shall be
the reported price for the next preceding day on which sales were made.

      Each employee who continues to be a participant in the Plan on the
Exercise Date shall be deemed to have exercised his Option at the Option Price
on such date and shall be deemed to have purchased from the Company the number
of full shares of Common Stock reserved for the purpose of the Plan that his
accumulated payroll deductions on such date will pay for, but not in excess of
the maximum number determined in the manner set forth above.

      Any balance remaining in an employee's payroll deduction account at the
end of a Plan Period will be automatically refunded to the employee, except that
any balance which is less than the purchase price of one share of Common Stock
will be carried forward into the employee's payroll deduction account for the
following Offering, unless the employee elects not to participate in the
following Offering under the Plan, in which case the balance in the employee's
account shall be refunded.

10. Issuance of Certificates. Certificates representing shares of Common Stock
purchased under the Plan may be issued only in the name of the employee, in the
name of the employee and another person of legal age as joint tenants with
rights of survivorship, or (in the Company's sole discretion) in the name of a
brokerage firm, bank or other nominee holder designated by the employee. The
Company may, in its sole discretion and in compliance with applicable laws,
authorize the use of book entry registration of shares in lieu of issuing stock
certificates.

11. Rights on Retirement, Death or Termination of Employment. In the event of a
participating employee's termination of employment prior to the last business
day of a Plan Period, no payroll deduction shall be taken from any pay due and
owing to an employee and the balance in the employee's account shall be paid to
the employee or, in the event of the employee's death, (a) to a beneficiary
previously designated in a revocable notice signed by the employee (with any
spousal consent required under state law) or (b) in the absence such a
designated beneficiary, to the executor or administrator of the employee's
estate or (c) if no such executor or administrator has been appointed to the
knowledge of the Company, to such other person(s) as the Company may, in its
discretion, designate. If, prior to the last business day of the Plan Period,
the Designated Subsidiary by which an employee is employed shall cease to be a
subsidiary of the Company, or if the employee is transferred to a subsidiary of
the Company that is not a


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Designated Subsidiary, the employee shall be deemed to have terminated
employment for the purposes of this Plan.

12. Optionees not Stockholders. No employee shall have any rights as a
stockholder with respect to any shares of Common Stock to be distributed with
respect to an Option until becoming the record holder or such shares.
Notwithstanding the foregoing, in the event the Company effects a split of the
Common Stock by means of a stock dividend (and the exercise price of and the
number of shares subject to such Option are adjusted as of the date of the
distribution of the dividend rather than as of the record date for such
dividend), then an optionee who is deemed to have exercised an Option between
the record date and the distribution date for such stock dividend shall be
entitled to receive, on the distribution date, the stock dividend with respect
to the shares of Common Stock.

13. Rights not Transferable. Rights under this Plan are not transferable by a
participating employee other than by will or the laws of descent and
distribution, and are exercisable during the employee's lifetime only by the
employee.

14. Application of Funds. All funds received or held by the Company under this
Plan may be combined with other corporate funds and may be used for any
corporate purpose.

15. Adjustment in Case of Changes Affecting Common Stock. In the event of a
subdivision of outstanding shares of Common Stock, or the payment of a dividend
in Common Stock, the number of shares approved for this Plan, and the share
limitation set forth in Section 9, shall be increased proportionately, and such
other adjustment shall be made as may be deemed equitable by the Board or the
Committee. In the event of any other change affecting the Common Stock, such
adjustment shall be made as may be deemed equitable by the Board or the
Committee to give proper effect to such event.

16. Merger. If the Company shall at any time merge or consolidate with another
corporation and the holders of the capital stock of the Company immediately
prior to such merger or consolidation continue to hold at least 80% by voting
power of the capital stock of the surviving corporation ("Continuity of
Control"), the holder of each Option then outstanding will thereafter be
entitled to receive at the next Exercise Date upon the exercise of such Option
for each share as to which such Option shall be exercised the securities or
property which a holder of one share of the Common Stock was entitled to upon
and at the time of such merger or consolidation, and the Board or the Committee
shall take such steps in connection with such merger or consolidation as the
Board or the Committee shall deem necessary to assure that the provisions of
Section 15 shall thereafter be applicable, as nearly as reasonably may be, in
relation to the said securities or property as to which such holder of such
Option might thereafter be entitled to receive thereunder.


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      In the event of a merger or consolidation of the Company with or into
another corporation which does not involve Continuity of Control, or of a sale
of all or substantially all of the assets of the Company while unexercised
Options remain outstanding under the Plan, all outstanding Options shall be
cancelled by the Board or the Committee as of the effective date of any such
transaction, provided that notice of such cancellation shall be given to each
holder of an Option, and each holder of an Option shall have the right to
exercise such Option in full based on payroll deductions then credited to his
account as of a date determined by the Board or the Committee, which date shall
not be less than ten (10) days preceding the effective date of such transaction.

17. Amendment of the Plan. The Board may at any time, and from time to time,
amend this Plan in any respect, except that (a) if the approval of any such
amendment by the shareholders of the Company is required by Section 423 of the
Code, such amendment shall not be effected without such approval, and (b) in no
event may any amendment be made which would cause the Plan to fail to comply
with Section 423 of the Code.

18. Sufficient Shares. In the event that the total number of shares of Common
Stock specified in elections to be purchased under any Offering plus the number
of shares purchased under previous Offerings under this Plan exceeds the maximum
number of shares issuable under this Plan, the Board or the Committee will allot
the shares then available on a pro rata basis.

19. Termination of the Plan. This Plan may be terminated at any time by the
Board. Upon termination of this Plan all amounts in the accounts of
participating employees shall be promptly refunded.

20. Governmental Regulations. The Company's obligation to sell and deliver
Common Stock under this Plan is subject to listing on a national stock exchange
or quotation on the Nasdaq National Market and the approval of all governmental
authorities required in connection with the authorization, issuance or sale of
such stock.

21. Governing Law. The Plan shall be governed by Massachusetts law except to the
extent that such law is preempted by federal law.

22. Issuance of Shares. Shares may be issued upon exercise of an Option from
authorized but unissued Common Stock, from shares held in the treasury of the
Company, or from any other proper source.

23. Notification Upon Sales of Shares Each employee agrees, by entering the
Plan, to promptly give the Company notice of any disposition of shares purchased
under the Plan where such disposition occurs within two years after the date of
grant of the Option pursuant to which such shares were purchased or one year
after the date of exercise of the Option.


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24. Withholding. Each employee shall, no later than the date of the event
creating the tax liability, make provision satisfactory to the Board for payment
of any taxes required by law to be withheld in connection with any transaction
related to Options granted to or shares acquired by such employee pursuant to
the Plan. The Company may, to the extent permitted by law, deduct any such taxes
from any payment of any kind otherwise due to an employee.

25. Effective Date. The effective date of the plan is June 1, 1999.

                           Adopted by the Board of Directors on February 10,
                           1999 and approved by the stockholders on February 17,
                           1999; Amended and Restated by the Board of Directors
                           on April 22, 1999; Amended and Restated by the Board
                           of Directors on August 1, 2002; Amended by the Board
                           of Directors on March 4, 2004 and by the stockholders
                           on May 13, 2004.



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