<PAGE>
                                                                    Exhibit 10.1

                              MKS INSTRUMENTS, INC.

              AMENDED AND RESTATED 1997 DIRECTOR STOCK OPTION PLAN

1.    Purpose.

      The purpose of this Amended and Restated 1997 Director Stock Option Plan
(the "Plan") of MKS Instruments, Inc., a Massachusetts corporation (the
"Company"), is to encourage ownership in the Company by non-employee directors
of the Company whose continued services are considered essential to the
Company's future progress and to provide them with a further incentive to remain
as directors of the Company.

2.    Administration.

      The Board of Directors shall supervise and administer the Plan. Grants of
stock options under the Plan and the amount and nature of the awards to be
granted shall be automatic in accordance with Section 5. However, all questions
of interpretation of the Plan or of any options issued under it shall be
determined by the Board of Directors and such determination shall be final and
binding upon all persons having an interest in the Plan.

3.    Participation in the Plan.

      Directors of the Company who are not employees of the Company or any
subsidiary of the Company shall be eligible to participate in the Plan.

4.    Stock subject to the Plan.

      (a) Definition of Common Stock. "Common Stock" means (i) prior to the
closing of the Company's initial public offering of common stock pursuant to an
effective registration statement under the Securities Act of 1933 ("IPO"), the
Class B Common Stock, no par value per share, of the Company, and (ii) from and
after the closing of the IPO, the Common Stock, no par value per share, of the
Company.

      (b) The maximum number of shares of the Company's Common Stock which may
be issued under the Plan shall be 200,000 shares, subject to adjustment as
provided in Section 7. All share amounts set forth in this Plan reflect all
stock splits effected prior to April 16, 2003 (the "Restatement Date").

      (c) If any outstanding option under the Plan for any reason expires or is
terminated without having been exercised in full, the shares allocable to the
unexercised portion of such option shall again become available for grant
pursuant to the Plan.

      (d) All options granted under the Plan shall be nonstatutory options not
entitled to special tax treatment under Section 422 of the Internal Revenue Code
of 1986, as amended to date and as it may be amended from time to time (the
"Code").

5.    Terms, Conditions and Form of Options.

      Each option granted under the Plan shall be evidenced by a written
agreement in such form as the Board of Directors shall from time to time
approve, which agreements shall comply with and be subject to the following
terms and conditions:
<PAGE>
      (a) Option Grant Dates. Options shall automatically be granted to all
eligible outside directors as follows:

            (i) each person who first becomes an eligible outside director after
the Restatement Date shall be granted an option to purchase 20,000 shares of
Common Stock on the date of his or her initial election to the Board of
Directors; and

            (ii) each eligible outside director then in office on the date of
each annual meeting of stockholders of the Company shall be granted an
additional option to purchase 12,000 shares of Common Stock on the date of each
such annual meeting of stockholders, provided that he or she was elected to
serve as a director of the Company at least six months prior to the date of such
meeting.

      (b) Option Exercise Price. The option exercise price per share for each
option granted under the Plan shall equal (i) the last reported sales price per
share of the Company's Common Stock on the Nasdaq National Market (or, if the
Common Stock is traded on a national securities exchange on the date of grant,
the reported closing sales price per share of the Common Stock on such exchange)
on the date of grant (or if no such price is reported on such date such price as
reported on the nearest preceding day), (ii) if the Common Stock is not traded
on the Nasdaq National Market or a national securities exchange, the fair market
value per share on the date of grant as determined by the Board of Directors or
(iii) the average of the closing bid and asked prices in the over-the-counter
market.

      (c) Transferability of Options. Except as the Board of Directors of the
Company may otherwise determine or provide in a written agreement entered into
in connection with the grant of an option under the Plan, options shall not be
sold, assigned, transferred, pledged or otherwise encumbered by the Optionee,
either voluntarily or by operation of law except by will or the laws of descent
and distribution, and during the life of the optionee and shall be exercisable
only by him. Reference to an optionee, to the extent relevant in the context,
shall include references to authorized transferees.

      (d) Vesting Period. Except as the Board may otherwise determine or provide
in a written agreement entered into in connection with the grant of an option
under the Plan, each option granted pursuant to paragraph (a)(i) of this Section
5 shall become exercisable in twelve (12) equal quarterly installments following
the date of grant. Each option granted pursuant to paragraph (a)(ii) of this
Section 5 shall become fully exercisable on the day prior to the first annual
meeting of stockholders of the Company following the date of grant (or if no
such meeting is held within thirteen (13) months after the date of grant, on the
thirteen-month anniversary of the date of grant).

      (e) Termination. Upon termination of an optionee's service as a director
of the Company, each option held by him which was granted prior to the
Restatement Date may be exercised during the three-month period following such
termination of service and each option held by him which was granted on or after
the Restatement Date may be exercised during the one-year period following such
termination of service, in each case as to the exercisable portion of such
option as of the date of termination, provided that (i) no option may be
exercised more than ten (10) years after the date of grant and (ii) in the event
an optionee ceases to serve as a director due to his death or disability (within
the meaning of Section 22(e)(3) of the Code or any successor provision), each
option may be exercised, with respect to options granted prior to the
Restatement Date, within the period of 180 days following the date the optionee
ceases to serve as a director, and, with respect to options granted on or after
the Restatement Date, within the one-year period following the date the optionee
ceases to serve as a director, in each case by the optionee or by the person to
whom the option is transferred by will, by the laws of descent and distribution,
or by written notice, as to the portion of the option that is exercisable on the
date of death or disability and as to the additional portion that would have
become exercisable on the next anniversary date of the date of grant of such
option.
<PAGE>
      (f) Exercise Procedure. Options may be exercised only by written notice to
the Company at its principal office accompanied by (i) payment in cash of the
full consideration for the shares as to which they are exercised or (ii) an
irrevocable undertaking, in form and substance satisfactory to the Company, by a
broker to deliver promptly to the Company sufficient funds to pay the exercise
price or delivery of irrevocable instructions, in form and substance
satisfactory to the Company, to a broker to deliver promptly to the Company cash
or a check sufficient to pay the exercise price.

      (g) Exercise by Representative Following Death of Director. An optionee,
by written notice to the Company, may designate one or more persons (and from
time to time change such designation), including his or her legal
representative, who, by reason of the director's death, shall acquire the right
to exercise all or a portion of the option. If the person or persons so
designated wish to exercise any portion of the option, they must do so within
the term of the option as provided herein. Any exercise by a representative
shall be subject to the provisions of the Plan.

6.    Limitation of Rights.

      (a) No Right to Continue as a Director. Neither the Plan, nor the granting
of an option nor any other action taken pursuant to the Plan, shall constitute
or be evidence of any agreement or understanding, express or implied, that the
Company will retain the optionee as a director for any period of time.

      (b) No Stockholders' Rights for Options. An optionee shall have no rights
as a stockholder with respect to the shares covered by his options until the
date of the issuance to him of a stock certificate therefor, and no adjustment
will be made for dividends or other rights (except as provided in Section 7) for
which the record date is prior to the date such certificate is issued.

7.    Changes in Common Stock.

      (a) If, at any time after the Restatement Date, the outstanding shares of
Common Stock are increased, decreased or exchanged for a different number or
kind of shares or other securities, or if additional shares or new or different
shares or other securities are distributed with respect to such shares of Common
Stock or other securities, through merger, consolidation, sale of all or
substantially all of the assets of the Company, reorganization,
recapitalization, reclassification, stock dividend, stock split, reverse stock
split or other distribution with respect to such shares of Common Stock, or
other securities, an appropriate and proportionate adjustment will be made in
(i) the maximum number and kind of shares reserved for issuance under the Plan,
(ii) the number and kind of shares or other securities issuable pursuant to
Sections 5(a)(i) and 5(a)(ii) above, (iii) the number and kind of shares or
other securities subject to then outstanding options under the Plan and (iv) the
price for each share subject to any then outstanding options under the Plan,
without changing the aggregate purchase price as to which such options remain
exercisable. No fractional shares will be issued under the Plan on account of
any such adjustments.

      (b) In the event of (i) a consolidation, merger or other reorganization in
which all of the outstanding shares of Common Stock are exchanged for
securities, cash or other property of any other corporation or business entity
or (ii) any sale of all or substantially all of the Company's assets (in either
event, an "Acquisition"), all options outstanding under the Plan immediately
prior to the effective date of such Acquisition shall become automatically
exercisable in full upon the effective date of such Acquisition.
<PAGE>
8.    Amendment of the Plan.

      The Board of Directors may suspend or discontinue the Plan or revise or
amend it in any respect whatsoever; provided, however, that without approval of
the stockholders of the Company no revision or amendment shall change the number
of shares subject to the Plan (except as provided in Section 7).

9.    Notice.

      Any written notice to the Company required by any of the provisions of the
Plan shall be addressed to the Chief Financial Officer of the Company and shall
become effective when it is received.

10.   Governing Law.

      The Plan and all determinations made and actions taken pursuant hereto
shall be governed by the laws of The Commonwealth of Massachusetts.

                                              Adopted by the Board of Directors
                                              on December 31, 1997;
                                              Approved by the Stockholders
                                              on January 9, 1998;
                                              Amendments and restatement
                                              approved by the Board of Directors
                                              on April 16, 2003