FORM OF TAX INDEMNIFICATION AGREEMENT

TAX INDEMNIFICATION AND S CORPORATION DISTRIBUTION AGREEMENT





This TAX INDEMNIFICATION AND S CORPORATION DISTRIBUTION AGREEMENT (the "Agreement") is entered into as of March ___, 1999 between MKS INSTRUMENTS, INC., a Massachusetts corporation (the "Company"), and the persons listed on Schedule A attached hereto (individually a "Stockholder" and collectively the "Stockholders"). Capitalized terms not otherwise defined have the meanings ascribed to them in Section 1.1.



WHEREAS, the Company and the Stockholders have entered into this Agreement as a condition to the Public Offering;



WHEREAS, the Company has been an "S corporation" (as defined in Section 1361(a)(1) of the Code) for federal tax purposes since July 1, 1987;



WHEREAS, the Company and the Stockholders understand that the Company's S corporation status will terminate upon the date of the Public Offering (the "Termination Date"), and, as a result, the Company will be a "C corporation" (as defined in Section 1361(a)(2) of the Code) beginning on the Termination Date;



WHEREAS, the Company will declare the AAA Dividend which will be payable as soon as possible on or after the Closing Date;



WHEREAS, the Company and the Stockholders wish to terminate this Agreement such that it has no effect should the Public Offering not occur;



NOW, THEREFORE, the parties agree as follows:





ARTICLE I



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1.1 DEFINITIONS. The following terms, as used herein, have the following meanings:



"AA Account" means the Company's "accumulated adjustments account," as

defined in Section 1368(e)(1) of the Code, as of the close of business

on the day before the Termination Date.



"AAA Dividend" means the dividend to be declared by the Company of all

of the undistributed AA Account.











"AAA Settlement Date" means the last day of the "post-termination transition period," as defined in Section 1377(b) of the Code, of the Company, except shall not include any extension of the post-termination transition period pursuant to Section 1377(b)(l)(C) as the result of a determination that the Company's election under Section 1362(a) had terminated earlier than the Closing Date.



"Closing Date" means the date on which the Public Offering closes.



"Code" means the Internal Revenue Code of 1986, as amended.



"C Short Year" means that portion of the S Termination Year of the Company beginning on the Termination Date and ending on the last day of the S Termination Year.



"C Taxable Year" means any taxable year (or portion thereof) of the Company, including the C Short Year, during which it is subject to taxation as a C corporation as defined in Section 1361(a)(2) of the Code.



"Final Determination" means the first to occur of



(i) the expiration of 30 days after IRS acceptance of a Waiver of

Restrictions on Assessment and Collection of Deficiency of Tax and

Acceptance of Overassessment on IRS Form 870 or 870-AD (or any successor

comparable form or the expiration of a comparable period with respect to

any comparable agreement or form under the laws of other jurisdictions);



(ii) a decision, judgment, decree, or other order by a court of competent

jurisdiction that is not subject to further judicial review and has become

final;



(iii)the execution of a closing agreement under Section 7121 of the Code

or the acceptance by the IRS of an offer in compromise under Section 7122

of the Code, or comparable agreements under the laws of other

jurisdictions;



(iv) the expiration of the time for filing a claim for refund or for

instituting suit in respect for a claim for refund disallowed in whole or

in part by the IRS or other relevant tax authority;



(v) any other final disposition of the tax liability for such period by

reason of the expiration of the applicable statute of limitations; or



(vi) any other event that the parties agree is final and irrevocable

determination of the liability at issue.













"Public Offering" means the public offering of the Company's Common Stock pursuant to the Registration Statement on Form S-1 originally filed by the Company with the Securities and Exchange Commission on January 28, 1999.



"Record Date" means the day prior to the date upon which the Company's Registration Statement on Form S-1, as amended, which was initially filed with the Securities and Exchange Commission on January 28, 1999, is declared effective by the Securities and Exchange Commission.



"S Short Year" means that portion of the S Termination Year beginning on the first day of such taxable year and ending on the day immediately preceding the Termination Date.



"S Taxable Year" means any taxable year (or portion thereof) of the Company, including the S Short Year, during which it is subject to taxation as an S corporation as defined in Section 1361(a)(1) of the Code.



"S Termination Year" shall mean the fiscal year of the Company that includes the Termination Date.



"Taxing Authority" means the United States Internal Revenue Service and any comparable state or foreign taxing authority.



"Termination Date" means the date on which the S corporation status of the Company will terminate pursuant to Section 1362(d) of the Code, which is expected to be the Closing Date.





ARTICLE II



TERMINATION OF S CORPORATION STATUS, ALLOCATION OF INCOME,

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DECLARATION OF AAA DIVIDEND AND ADJUSTMENT OF AAA DIVIDEND

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2.1 TERMINATION OF S CORPORATION STATUS. The Company and the Stockholders understand that the Company's S corporation status will terminate upon the consummation of the Public Offering.



2.2 PRO RATA ALLOCATION OF TAX ITEMS. The Company shall be required to allocate the tax items described in Section 1362(e)(2)(A) of the Code between the S Short Year and the C Short Year pursuant to the pro rata allocation rules set forth in Section 1362(e)(2)(B) of the Code.



2.3 DECLARATION OF AAA DIVIDEND. Prior to the Closing Date, the Company shall declare the AAA Dividend, subject to the closing of the Public Offering, to the











stockholders of record on the Record Date payable as soon as possible on or after the Closing Date.



2.4 ADJUSTMENT TO AAA DIVIDEND.



(a) The parties acknowledge that the amount of the AAA Dividend will be based on good faith determinations by the Company of the amount of AA Account as of the Termination Date.



(b) The parties agree that if the Company determines after the Termination Date and on or before the AAA Settlement Date that the amount of the AA Account as of the Termination Date does not equal the amount of the AAA Dividend, then:



(i) if the amount of the AAA Dividend exceeds the amount of AA

Account as of the Termination Date, the Stockholders who received the

AAA Dividend shall thereafter remit to the Company their pro-rata

share of such excess no later than thirty (30) days after receiving

notice from the Company that such amount is payable; and



(ii) if the amount of the AA Account as of Termination Date

exceeds the amount of the AAA Dividend, the Company shall thereafter

distribute to the Stockholders their pro-rata shares of such excess

within thirty (30) days following the date the Company determines an

amount is payable pursuant to this Section 2.4(b)(ii).



(c) Any payment due under this section shall be increased by interest on the amount of such payment computed from the date of the payment of the AAA Dividend until the date of payment pursuant to this section. The interest rate shall be the Prime Rate of BankBoston (or its successors) as adjusted from time to time.





ARTICLE III



TAX PAYMENTS AND INDEMNIFICATION OBLIGATIONS

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3.1 LIABILITY FOR TAXES INCURRED DURING S SHORT YEAR. Each Stockholder covenants and agrees that: (i) the Stockholder will duly include, in his own federal and state income tax returns, all items of income, gain, loss, deduction, or credit attributable to the S Short Year in a manner consistent with the Form 1120S and the schedules thereto (and the corresponding state income tax forms and schedules) to be filed by the Company with respect to such period; (ii) such returns shall be filed no later than the due date (incl ...