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                                                                   EXHIBIT 10.31

                           SILICON VALLEY GROUP, INC.

                      CHANGE OF CONTROL SEVERANCE AGREEMENT

     This Change of Control Severance Agreement (the "Agreement") is made and
entered into effective as of September 23, 1999 (the "Effective Date"), by and
between Jeffery Kowalski, President Thermal Systems, (the "Employee") and
Silicon Valley Group, Inc., a Delaware corporation (the "Company"). Certain
capitalized terms used in this Agreement are defined in Section I below.

                                    RECITALS

     A.   It is expected that he Company from time to time will consider the
possibility of a Change of Control. The Board of Directors of the Company (the
"Board") recognizes that such consideration can be a distraction to the Employee
and can cause the Employee to consider alternative employment opportunities.

     B.   The Board believes that it is in the best interests of the Company and
its shareholders to provide the Employee with an incentive to continue his
employment and to maximize the value of the Company upon a Change of Control for
the benefit of its shareholders.

     C.   In order to provide the Employee with enhanced financial security and
sufficient encouragement to remain with the Company notwithstanding the
possibility of a Change of Control, the Board believes that it is imperative to
provide the Employee with certain severance benefits upon the Employees
termination of employment following a Change of Control.

                                    AGREEMENT

     In consideration of the mutual covenants herein contained and the continued
employment of Employee by the Company, the parties agree as follows:

     1.   Definition of Terms. The following terms referred to in this Agreement
shall have the following meanings:

          (a)  Cause. "Cause" shall mean (i) any act of personal dishonesty
taken by the Employee in connection with his responsibilities as an employee
which is intended to result in substantial personal enrichment of the Employee,
(ii) Employee's conviction of a felony, (iii) a willful act by the Employee
which constitutes gross misconduct and is injurious to the Company, and (iv)
continued violations by the Employee of the Employee's obligations to the
Company which are demonstrably willful and deliberate on the Employee's part
after (a) there has been delivered to the Employee a written demand for
performance from the Company which describes the basis for the Company's belief
that the Employee has not substantially performed his duties and sets forth
specific

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          (b)  Change of Control. "Change of Control" shall mean the occurrence
of any of the following events:

               (i)  Any person" (as such term is used in Sections 13(d) and
14(d) of the Securities Exchange Act of 1934, as amended) is or becomes the
beneficial owner" (as defined in Rule I 3d-3 under said Act), directly or
indirectly, of securities of the Company representing fifty percent (50%) or
more of the total voting power represented by the Company's then outstanding
voting securities ;or

               (ii) A change in the composition of the Board occurring within a
two-year period, as a result of which fewer than a majority of the directors are
Incumbent Directors. "Incumbent Directors" shall mean directors who either (A)
are directors of the Company as of the date hereof, or (B) are elected, or
nominated for election, to the Board with the affirmative votes of at least a
majority of the Incumbent Directors at the time of such election or nomination
(but shall not include an individual whose election or nomination is in
connection with an actual or threatened proxy contest relating to the election
of directors to the Company); or

               (iii) The consummation of a merger or consolidation of the
Company with any other corporation, other than a merger or consolidation which
would result in the voting securities of the Company outstanding immediately
prior thereto continuing to represent (either by remaining outstanding or by
being converted into voting securities of the surviving entity) at least fifty
percent (50%) of the total voting power represented by the voting securities of
the Company or such surviving entity outstanding immediately after such merger
or consolidation, or the stockholders of the Company approve a plan of complete
liquidation of the Company or the consummation of the sale or disposition by the
Company of all or substantially all the Company's assets.

          (c)  Disability. "Disability" shall mean that the Employee has been
unable to perform his duties under this Agreement, with or without reasonable
accommodation, as a result of his incapacity due to physical or mental illness,
and such inability, at least 26 weeks after its commencement, is determined to
be total and permanent by a physician selected by the Company or its insurers
and agreed to the Employee or the Employee's legal representative (such
agreement not to be unreasonably withheld). Termination resulting from
Disability may only be effected after at least 30 days written notice by the
Company of its intention to terminate the Employee's employment. In the event
that the Employee resumes the performance of substantially all of his duties
hereunder before the termination of his employment becomes effective, the notice
of intent to terminate shall automatically be deemed to have been revoked.

          (d)  Involuntary Termination. "Involuntary Termination" shall mean any
of the following: (i) without the Employee's express written consent, the
assignment to the Employee of any duties or the reduction of the Employee's
duties, either of which results in a significant diminution in the Employee's
position or responsibilities with the Company in effect immediately prior to
such assignment, or the removal of the Employee from such position and
responsibilities; (ii)


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a substantial reduction, without good business reasons and without the
Employee's written consent, of the facilities and perquisites (including office
space and location) available to the Employee immediately prior to such
reduction; (iii) a reduction by the Company in the Base Compensation of the
Employee as in effect immediately prior to such reduction, other than (A) a
bonus reduction resulting from application of a bonus formula or plan on a basis
that is consistent with prior practice or (B) a reduction which is comparable
(on a percentage basis) to a reduction applicable to all executive officers of
the Company; (iv) a material reduction by the Company in the kind or level of
employee benefits to which the Employee is entitled immediately prior to such
reduction with the result that the Employee's overall benefits package is
Significantly reduced other than, so long as there is no Change of Control, a
reduction which is comparable to a reduction applicable to all executive
officers of the Company; (v) the relocation of the Employee to a facility or a
location more than 25 miles from the Employee's then present location, without
the Employee's express written consent; (vi) any purported termination of the
Employee by the Company which is not effected for Cause, or any purported
termination for which the grounds relied upon are not valid; (vii) the failure
of the Company to obtain the assumption of this agreement by any successors
contemplated in Section 9 below; (viii) any termination due to the death or
Disability of Employee; or (ix) any purported termination of the Employee's
employment by the Company which is not effected pursuant to a notice of
termination satisfying the requirements of Section 8(b) below, and for purposes
of this Agreement, no such purported termination shall be effective.

          (e)  Termination Date. "Termination Date" shall mean the effective
date of any notice of termination delivered by one party to the other hereunder.

     2.   Term of Agreement. This Agreement shall terminate upon the later of
(i) the date that all obligations of the parties hereto under this Agreement
have been satisfied, (ii) twelve (12) months after a Change of Control or (iii)
three (3) years after the Effective Date of this Agreement.

     3.   At-Will Employment. The Company and the Employee acknowledge that the
Employee's employment is and shall continue to be at-will, as defined under
applicable law. If the Employee's employment terminates for any reason, the
Employee shall not be entitled to any payments, benefits, damages, awards or
compensation other than as provided by this Agreement, or as may otherwise be
established under the Company's then existing employee benefit plans or policies
at the time of termination.

     4.   Severance Benefits.

          (a)  Termination Following A Change of Control.

               (i)  Involuntary Termination. If the Employee's employment with
the Company terminates as a result of an Involuntary Termination at any time
within twelve (12) months after a Change of Control, the Employee shall be
entitled to receive continuing payments of severance pay for eighteen (18)
months at a rate equal to the Employee's base salary (calculated based on the
twelve (12) month period preceding the Termination Date) and car allowance. Such


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severance payments shall be paid monthly in accordance with the Company's normal
payroll practices. In addition, Employee shall be entitled to receive Employee's
bonus for the year, prorated for the portion of the year Employee was employed
by the Company and payable after the end of the Company's fiscal year and to the
extent Employee achieved his performance criteria. If Employee dies after an
Involuntary Termination described in this Section, his estate or designated
beneficiary shall continue to receive the remaining payments as provided for in
this Section.

               (ii) Other Termination. If the Employee's employment with the
Company terminates other than as a result of an Involuntary Termination at any
time within twelve (12) months after a Change of Control, then the Employee
shall not be entitled to receive severance or other benefits hereunder, but may
be eligible for those benefits (if any) as may then be established under the
Company's then existing severance and benefits plans and policies at the
Termination Date.

          (b)  Termination Apart from a Change of Control. If the Employee's
employment with the Company terminates for any or no reason other than within
the twelve (12) months following a Change of Control, then the Employee shall
not be entitled to receive severance or other benefits hereunder, but may be
eligible for those benefits (if any) as may then be established under the
Company's then existing severance and benefits plans and policies at the time of
such termination.

          (c)  Accrued Wages and Vacation: Expenses. Without regard to the
reason for, or the timing of Employee's termination of employment: (i) the
Company shall pay the Employee any unpaid base salary due for periods prior to
the Termination Date; (ii) the Company shall pay the Employee all of the
Employee's accrued and unused vacation through the Termination Date; and (iii)
following submission of proper expense reports by the Employee, the Company
shall reimburse the Employee for all expenses reasonably and necessarily
incurred by the Employee in connection with the business of the Company prior to
the Termination Date. These payments shall be made promptly upon termination and
within the period of time mandated by law.

          (d)  Set-off. If in the event of termination of Employee's employment
for any reason Employee owes any amounts to the Company, the Company shall be
permitted to (i) reduce the amount of each monthly severance payment, if any, to
be paid to Employee by the amount of all accrued interest on, and a portion of
the outstanding principal amount of, any such debt owing from Employee to the
Company on the Termination Date, or (ii) reduce the amount Employee will receive
in any single, lump sum, if any, by the outstanding principal amount and accrued
interest of any such debt owing from Employee to the Company on the Termination
Date. The portion of the principal amount of such debt by which each monthly
severance payment will be reduced shall be 1/18 in the case of a termination
covered by Section 4(a)(i).

     5.   Option Acceleration. If the Employee's employment with the Company
terminates as a result of an Involuntary Termination at any time within twelve
(12) months after a Change of Control, any unvested outstanding stock options
granted to the Employee by the Company shall


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become fully vested and exercisable as of the Termination Date. Such Options
shall remain exercisable for ninety (90) days after the Termination Date.

     6.   Limitation on Payments.

          (a)  Certain Business Combinations. In the event it is determined by
the Board, upon receipt of a written opinion of the Company's independent public
accountants, that the enforcement of any Section or subsection of this
Agreement, including, but not limited to, Section (d) hereof, which allows for
the acceleration of vesting of options to purchase shares of the Company's
common stock upon a termination in connection with a Change of Control, would
preclude accounting for any proposed business combination of the Company
involving a Change of Control as a pooling of interests, and the Board otherwise
desires to approve such a proposed business transaction which requires as a
condition to the closing of such transaction that it be accounted for as a
polling of interests, then any such Section of this Agreement shall be null and
void, but only if the absence of enforcement of such Section would preserve the
pooling treatment. For purposes of this Section, the Board's determination shall
require the unanimous approval of the disinterested Board members.

          (b)  Golden Parachute Excise Tax.

               (i)  In the event that the severance and other benefits provided
for in this Agreement or otherwise payable to the Executive (i) constitute
"parachute payments" within the meaning of Section 280G of the Internal Revenue
Code of 1986, as amended (the "Code") and (ii) but for this Section would be
subject to the excise tax imposed by Section 4999 of the Code, then the
Executive's severance benefits under Sections 4 and 5 shall be payable either
(i) in full, or (ii) as to such lesser amount which would result in no portion
of such severance benefits being subject to excise tax under Section 4999 of the
Code, whichever of the foregoing amounts, taking into account the applicable
federal, state and local income taxes and the excise tax imposed by Section
4999, results in the receipt by the Executive on an after-tax basis, of the
greatest amount of severance benefits under this Agreement, notwithstanding that
all or some portion of such severance benefits may be taxable under Section 4999
of the Code.

               (ii) If a reduction in the payments and benefits that would
otherwise be paid or provided to the Executive under the terms of this Agreement
is necessary to comply with the provisions of Section 6(a), the Executive shall
be entitled to select which payments or benefits will be reduced and the manner
and method of any such reduction of such payments or benefits (including but not
limited to the number of options that would vest under Section 5 subject to
reasonable limitations (including, for example, express provisions under the
Company's benefit plans) (so long as the requirements of Section 6(a) are met).
Within thirty (30) days after the amount of any required reduction in payments
and benefits is finally determined in accordance with the provisions of Section
6(c), the Executive shall notify the Company in writing regarding which payments
or benefits are to be reduced. If the Executive gives no notification, the
Company will determine which amounts to reduce. If; as a result of any reduction
required by Section 6(a),

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amounts previously paid to the Executive exceed the amount to which the
Executive is entitled, the Executive will promptly return the excess amount to
the Company.

               (iii) Unless the Company and the Executive otherwise agree in
writing, any determination required under this Section shall be made in writing
by the Company's independent public accountants (the "Accountants"), whose
determination shall be conclusive and binding upon the Executive and the Company
for all purposes. For purposes of making the calculations required by this
Section, the Accountants may make reasonable assumptions and approximations
concerning applicable taxes and may rely on reasonable, good faith
interpretations concerning the application of Sections 280G and 4999 of the
Code. The Company and the Executive shall furnish to the Accountants such
information and documents as the Accountants may reasonably request in order to
make a determination under this Section. The Company shall bear all costs the
Accountants may reasonably incur in connection with any calculations
contemplated by this Section.

     7.   Successors.

          (a)  ComDanv1s Successors. Any successor to the Company (whether
direct or indirect and whether by purchase, lease, merger, consolidation,
liquidation or otherwise) to all or substantially all of the Company's business
and/or assets shall assume the Company's obligations under this Agreement and
agree expressly to perform the Company's obligations under this Agreement in the
same manner and to the same extent as the Company would be required to perform
such obligations in the absence of a succession. For all purposes under this
Agreement, the term "Company" shall include any successor to the Company's
business and/or assets which executes and delivers the assumption agreement
described in this subsection (a) or which becomes bound by the terms of this
Agreement by operation of law.

          (b)  Employee's Successors. Without the written consent of the
Company, Employee shall not assign or transfer this Agreement or any right or
obligation under this Agreement to any other person or entity. Notwithstanding
the foregoing, the terms of this Agreement and all rights of Employee hereunder
shall inure to the benefit of; and be enforceable by, Employee's personal or
legal representatives, executors, administrators, successors, heirs,
distributees, devisees and legatees.

     8.   Notices.

          (a)  General. Notices and all other communications contemplated by
this Agreement shall be in writing and shall be deemed to have been duly given
when personally delivered or when mailed by U.S. registered or certified mail,
return receipt requested and postage prep aid. In the case of the Employee,
mailed notices shall be addressed to him at the home address which he most
recently communicated to the Company in writing. In the case of the Company,
mailed notices shall be addressed to its corporate headquarters, and all notices
shall be directed to the attention of its Secretary.


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          (b)  Notice of Termination. Any termination by the Company for Cause
or by the Employee as a result of a voluntary resignation or an Involuntary
Termination shall be communicated by a notice of termination to the other party
hereto given in accordance with this Section. Such notice shall indicate the
specific termination provision in this Agreement relied upon, shall set forth in
reasonable detail the facts and circumstances claimed to provide a basis for
termination under the provision so indicated, and shall specify the Termination
Date (which shall be not more than 30 days after the giving of such notice). The
failure by the Employee to include in the notice any fact or circumstance which
contributes to a showing of Involuntary Termination shall not waive any right of
the Employee hereunder or preclude the Employee from asserting such fact or
circumstance in enforcing his rights hereunder.

     9.   Arbitration.

          (a)  Any dispute or controversy arising out of; relating to, or in
connection with this Agreement, or the interpretation, validity, construction,
performance, breach, or termination thereof; shall be settled by binding
arbitration to be held in San Francisco County, California, in accordance with
the National Rules for the Resolution of Employment Disputes then in effect of
the American Arbitration Association (the "Rules"). The arbitrator may grant
injunctions or other relief in such dispute or controversy. The decision of the
arbitrator shall be final, conclusive and binding on the parties to the
arbitration. Judgment may be entered on the arbitrator's decision in any court
having jurisdiction.

          (b)  The arbitrator(s) shall apply California law to the merits of any
dispute or claim, without reference to conflicts of law rules. The arbitration
proceedings shall be governed by federal arbitration law and by the Rules,
without reference to state arbitration law. Employee hereby consents to the
personal jurisdiction of the state and federal courts located in California for
any action or proceeding arising from or relating to this Agreement or relating
to any arbitration in which the parties are participants.

          (c)  Employee understands that nothing in this Section modifies
Employee's at-will employment status. Either Employee or the Company can
terminate the employment relationship at any time, with or without cause.

          (d)  EMPLOYEE HAS READ AND UNDERSTANDS THIS SECTION, WHICH DISCUSSES
ARBITRATION. EMPLOYEE UNDERSTANDS THAT SUBMITTING ANY CLAIMS ARISING OUT OF,
RELATING TO, OR IN CONNECTION WITH THIS AGREEMENT, OR THE INTERPRETATION,
VALIDITY, CONSTRUCTION, PERFORMANCE, BREACH OR TERMINATION THEREOF TO BINDING
ARBITRATION, CONSTITUTES A WAIVER OF EMPLOYEE'S RIGHT TO A JURY TRIAL AND
RELATES TO THE RESOLUTION OF ALL DISPUTES RELATING TO ALL ASPECTS OF THE
EMPLOYER/EMPLOYEE RELATIONSHIP, INCLUDING BUT NOT LIMITED TO, THE FOLLOWING
CLAIMS:


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               (i)  ANY AND ALL CLAIMS FOR WRONGFUL DISCHARGE OF EMPLOYMENT;
BREACH OF CONTRACT, BOTH EXPRESS AND IMPLIED; BREACH OF THE COVENANT OF GOOD
FAITH AND FAIR DEALING, BOTH EXPRESS AND IMPLIED; NEGLIGENT OR INTENTIONAL
INFLICTION OF EMOTIONAL DISTRESS; NEGLIGENT OR INTENTIONAL MISREPRESENTATION;
NEGLIGENT OR INTENTIONAL INTERFERENCE WITH CONTRACT OR PROSPECTIVE ECONOMIC
ADVANTAGE; AND DEFANIATION.

               (ii) ANY AND ALL CLAIMS FOR VIOLATION OF ANY FEDERAL STATE OR
MUNICIPAL STATUTE, INCLUDING, BUT NOT LIMITED TO, TITLE VII OF THE CIVIL RIGHTS
ACT OF 1964, THE CIVIL RIGHTS ACT OF 1991, THE AGE DISCRIMINATION IN EMPLOYMENT
ACT OF 1967, THE AMERICANS WITH DISABILITIES ACT OF 1990, THE FAIR LABOR
STANDARDS ACT, THE CALIFORNIA FAIR EMPLOYMENT AND HOUSING ACT, AND LABOR CODE
SECTION 201, et seq;

               (iii) ANY AND ALL CLAIMS ARISING OUT OF ANY OTHER LAWS AND
REGULATIONS RELATING TO EMPLOYMENT OR EMPLOYMENT DISCRIMINATION.

     10.  Miscellaneous Provisions.

          (a)  No Duty to Mitigate. The Employee shall not be required to
mitigate the amount of any payment contemplated by this Agreement, nor shall any
such payment be reduced by any earnings that the Employee may receive from any
other source.

          (b)  Waiver. No provision of this Agreement may be modified, waived or
discharged unless the modification, waiver or discharge is agreed to in writing
and signed by the Employee and by an authorized officer of the Company (other
than the Employee). No waiver by either party of any breach of; or of compliance
with, any condition or provision of this Agreement by the other party shall be
considered a waiver of any other condition or provision or of the same condition
or provision at another time.

          (c)  Integration. This Agreement and the stock option agreements
representing the Options represent the entire agreement and understanding
between the parties as to the subject matter herein and supersede all prior or
contemporaneous agreements, whether written or oral.

          (d)  Choice of Law. The validity, interpretation, construction and
performance of this Agreement shall be governed by the internal substantive
laws, but not the conflicts of law rules, of the State of California.

          (e)  Severability. The invalidity or unenforceability of any provision
or provisions of this Agreement shall not affect the validity or enforceability
of any other provision hereof; which shall remain in full force and effect.


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          (f)  No Assignment of Benefits. The rights of any person to payments
or benefits under this Agreement shall not be made subject to option or
assignment, either by voluntary or involuntary assignment or by operation of
law, including (without limitation) bankruptcy, garnishment, attachment or other
creditor's process, and any action in violation of this subsection (g) shall be
void.

          (g)  Employment Taxes. All payments made pursuant to this Agreement
will be subject to withholding of applicable taxes.

          (h)  Assignment by Company. The Company may assign its rights under
this Agreement to an affiliate, and an affiliate may assign its rights under
this Agreement to another affiliate of the Company or to the Company; provided,
however, that no assignment shall be made if the net worth of the assignee is
less than the net worth of the Company at the time of assignment. In the case of
any such assignment, the term Company" when used in a Section of this Agreement
shall mean the corporation that actually employs the Employee.

          (i)  Counterparts. This Agreement may be executed in counterparts,
each of which shall be deemed an original, but all of which together will
constitute one and the same instrument.

     IN WITNESS WHEREOF, each of the parties has executed this Agreement, in the
case of the Company by its duly authorized officer, as of the day and year first
above written.

COMPANY:                                SILICON VALLEY GROUP, INC.

                                        By: /s/ Papken S. Der Torossian
                                           -------------------------------------
                                        Title: Chairman & CEO
                                              ----------------------------------
EMPLOYEE:                               /s/ Jeffrey Kowalski
                                        ----------------------------------------


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