<PAGE>
                                                                  Exhibit 10.31
                         NUMERICAL TECHNOLOGIES, INC.

                                2000 STOCK PLAN

                   STOCK OPTION AGREEMENT -- EARLY EXERCISE

     Unless otherwise defined herein, the terms defined in the Plan shall have
the same defined meanings in this Option Agreement.

I.   NOTICE OF STOCK OPTION GRANT
     ----------------------------

     Yao-Ting Wang

     You have been granted an option to purchase Common Stock of the Company,
subject to the terms and conditions of the Plan and this Option Agreement, as
follows:

     Date of Grant:                           February 1, 2000

     Vesting Commencement Date:               February 1, 2000

     Exercise Price per Share:                   $        4.00

     Total Number of Shares Granted:                   333,333

     Total Exercise Price:                       $1,333,332.00

     Type of Option:            _____   Incentive Stock Option

                                X    Nonstatutory Stock Option
                              -----

     Term/Expiration Date:           Ten Years/February 1, 2010*

_______________
*  Or earlier, pursuant to the termination period set forth below.

     Exercise and Vesting Schedule:
     -----------------------------

     This Option is exercisable immediately, in whole or in part, and shall vest
according to the following vesting schedule:

     One-fourth (1/4th) of the Shares subject to the Option shall vest twelve
months after the Vesting Commencement Date, and one-sixteenth (1/16th) of the
Shares subject to the Option shall vest on the last day of each three month
anniversary thereafter, subject to your continuing to be a Service Provider on
such dates.
<PAGE>

     Change of Control; Constructive Termination:
     -------------------------------------------

     Notwithstanding the provisions of Section 14(c) of the Plan, if the Company
merges with or into another entity, sells all or substantially all of its
assets, or enters into any other similar transaction or reorganization
(including without limitation, a sale of stock of the Company) as a result of
which the shareholders of the Company immediately prior to such transaction will
not hold at least 50% of the voting power of the surviving, purchasing or
continuing entity, as applicable (taking into account any securities issued to
the shareholders of the Company in the transaction) (a "Change of Control
Transaction"), then on the six month anniversary of the Change of Control
Transaction (the "Anniversary Date") fifty percent (50%) of the Shares subject
to the Option which have not vested as of the Anniversary Date shall become
fully vested and exercisable.  The Board shall notify the Optionee at least
fifteen (15) days prior to the closing of a Change of Control Transaction, and
such notification shall include a statement as to whether or not the Option will
be assumed by the surviving or purchasing entity or whether an equivalent
substitute option will be provided by such entity.

     Following an assumption or substitution of the Option in connection with a
Change of Control Transaction, if the Optionee's status as an Employee of the
successor corporation is terminated by the successor corporation as a result of
an Involuntary Termination (as defined below) within twelve months following the
Change of Control Transaction, the Optionee shall fully vest in and have the
right to exercise the Option as to all of the Shares, including Shares as to
which the Option would not otherwise be vested or exercisable.

     Any of the following events shall constitute an "Involuntary Termination":
(i) without the Optionee's express written consent, a significant reduction of
the Optionee's duties, authority and responsibilities, relative to the
Optionee's duties, authority and responsibilities as in effect immediately prior
to the Change of Control Transaction; (ii) a material reduction in the base
salary of the Optionee as in effect immediately prior to the Change of Control
Transaction; (iii) a material reduction in the kind or level of employee
benefits, including bonuses, to which the Optionee was entitled immediately
prior to the Change of Control Transaction with the result that the Optionee's
overall benefits package is significantly reduced; (iv) the relocation of the
Optionee to a facility or a location more than sixty (60) miles from the
Optionee's then present location, without the Optionee's express written
consent; (v) any purported termination of the Optionee which is not effected for
Disability or for Cause (as defined below), or any purported termination for
which the grounds relied upon are not valid; (vi) or any act or set of facts or
circumstances which would, under California case law or statute, constitute a
constructive termination of the Optionee.

     "Cause" shall mean (i) any act of personal dishonesty taken by the Optionee
in connection with his responsibilities as a Service Provider and intended to
result in substantial personal enrichment of the Optionee, (ii) Optionee's
conviction of a felony, (iii) a willful act by the Optionee which constitutes
gross misconduct and which is injurious to the Successor Corporation, and (iv)
following delivery to the Optionee of a written demand for performance from the
Successor Corporation which describes the basis for the Successor Corporation's
belief that the Optionee has not substantially performed his duties, continued
violations by the Optionee of the Optionee's

                                      -2-
<PAGE>

obligations to the Successor Corporation which are demonstrably willful and
deliberate on the Optionee's part.

     Termination Period:
     ------------------

     You may exercise this Option for thirty days after you cease to be a
Service Provider.  Upon your death or disability, this Option may be exercised
for one year after you cease to be a Service Provider.  In no event may you
exercise this Option after the Term/Expiration Date as provided above.

II.  AGREEMENT
     ---------

     1.   Grant of Option. The Plan Administrator of the Company hereby grants
          ---------------
to the Optionee named in the Notice of Grant (the "Optionee"), an option (the
"Option") to purchase the number of Shares set forth in the Notice of Grant, at
the exercise price per Share set forth in the Notice of Grant (the "Exercise
Price"), and subject to the terms and conditions of the Plan, which is
incorporated herein by reference. Subject to Section 17(c) of the Plan, in the
event of a conflict between the terms and conditions of the Plan and this Option
Agreement, the terms and conditions of the Plan shall prevail.

          If designated in the Notice of Grant as an Incentive Stock Option
("ISO"), this Option is intended to qualify as an Incentive Stock Option as
defined in Section 422 of the Code.  Nevertheless, to the extent that it exceeds
the $100,000 rule of Code Section 422(d), this Option shall be treated as a
Nonstatutory Stock Option ("NSO").

     2.   Exercise of Option.  This Option shall be exercisable during its term
          ------------------
in accordance with the provisions of Section 10 of the Plan as follows:

          (a)  Right to Exercise.
               -----------------

                    (i)    Subject to subsections 2(a)(ii) and 2(a)(iii) below,
this Option shall be exercisable cumulatively according to the vesting schedule
set forth in the Notice of Grant. Alternatively, at the election of the
Optionee, this option may be exercised in whole or in part at any time as to
Shares which have not yet vested. For purposes of this Stock Option Agreement,
Shares subject to the Option shall vest based on continued employment of
Optionee with the Company. Vested Shares shall not be subject to the Company's
repurchase right (as set forth in the Restricted Stock Purchase Agreement,
attached hereto as Exhibit E-1).
                   -----------

                    (ii)   As a condition to exercising this Option for unvested
Shares, the Optionee shall execute the Restricted Stock Purchase Agreement.

                    (iii)  This Option may not be exercised for a fraction of a
Share.

          (b)  Method of Exercise.  This Option shall be exercisable by
               ------------------
delivery of an exercise notice in the form attached as Exhibit A (the
                                                       ---------
"Exercise Notice") which shall state the election to exercise the Option, the
number of Shares with respect to which the Option is being exercised (the
"Exercised Shares"), and such other representations and agreements as may be
required by the

                                      -3-
<PAGE>

Company. The Exercise Notice shall be accompanied by payment of the aggregate
Exercise Price as to all Exercised Shares. This Option shall be deemed to be
exercised upon receipt by the Company of such fully executed Exercise Notice
accompanied by the aggregate Exercise Price.

          No Shares shall be issued pursuant to the exercise of an Option unless
such issuance and such exercise complies with Applicable Laws.  Assuming such
compliance, for income tax purposes the Shares shall be considered transferred
to the Optionee on the date on which the Option is exercised with respect to
such Shares.

     3.   Optionee's Representations.  In the event the Shares have not been
          --------------------------
registered under the Securities Act of 1933, as amended, at the time this Option
is exercised, the Optionee shall, if required by the Company, concurrently with
the exercise of all or any portion of this Option, deliver to the Company his or
her Investment Representation Statement in the form attached hereto as Exhibit
                                                                       -------
B.
-

     4.   Lock-Up Period.  Optionee hereby agrees that, if so requested by the
          --------------
Company or any representative of the underwriters (the "Managing Underwriter")
in connection with any registration of the offering of any securities of the
Company under the Securities Act, Optionee shall not sell or otherwise transfer
any Shares or other securities of the Company during the 180-day period (or such
other period as may be requested in writing by the Managing Underwriter and
agreed to in writing by the Company) (the "Market Standoff Period") following
the effective date of a registration statement of the Company filed under the
Securities Act. Such restriction shall apply only to the first registration
statement of the Company to become effective under the Securities Act that
includes securities to be sold on behalf of the Company to the public in an
underwritten public offering under the Securities Act. The Company may impose
stop-transfer instructions with respect to securities subject to the foregoing
restrictions until the end of such Market Standoff Period.

     5.   Method of Payment.  Payment of the aggregate Exercise Price shall be
          -----------------
by any of the following, or a combination thereof, at the election of the
Optionee:

          (a)  cash;

          (b)  check;

          (c)  consideration received by the Company under a formal cashless
exercise program adopted by the Company in connection with the Plan;

          (d)  surrender of other Shares which, (i) in the case of Shares
acquired upon exercise of an option, have been owned by the Optionee for more
than six (6) months on the date of surrender, and (ii) have a Fair Market Value
on the date of surrender equal to the aggregate Exercise Price of the Exercised
Shares; or

          (e)  with the Administrator's consent, delivery of Optionee's
promissory note (the "Note") in the form attached hereto as Exhibit D, in the
amount of the aggregate Exercise Price of the Exercised Shares together with the
execution and delivery by the Optionee of the Security Agreement attached hereto
as Exhibit C. The Note shall bear interest at the "applicable federal rate"

                                      -4-
<PAGE>

prescribed under the Code and its regulations at time of purchase, and shall be
secured by a pledge of the Shares purchased by the Note pursuant to the Security
Agreement.

     6.   Restrictions on Exercise.  This Option may not be exercised until
          ------------------------
such time as the Plan has been approved by the shareholders of the Company, or
if the issuance of such Shares upon such exercise or the method of payment of
consideration for such shares would constitute a violation of any Applicable
Law.

     7.   Non-Transferability of Option.  This Option may not be transferred in
          -----------------------------
any manner otherwise than by will or by the laws of descent or distribution and
may be exercised during the lifetime of Optionee only by Optionee. The terms of
the Plan and this Option Agreement shall be binding upon the executors,
administrators, heirs, successors and assigns of the Optionee.

     8.   Term of Option.  This Option may be exercised only within the term
          --------------
set out in the Notice of Grant, and may be exercised during such term only in
accordance with the Plan and the terms of this Option.

     9.   Tax Consequences.  Set forth below is a brief summary as of the date
          ----------------
of this Option of some of the federal tax consequences of exercise of this
Option and disposition of the Shares. THIS SUMMARY IS NECESSARILY INCOMPLETE,
AND THE TAX LAWS AND REGULATIONS ARE SUBJECT TO CHANGE. THE OPTIONEE SHOULD
CONSULT A TAX ADVISER BEFORE EXERCISING THIS OPTION OR DISPOSING OF THE SHARES.

          (a)  Exercise of ISO.  If this Option qualifies as an ISO, there will
               ---------------
be no regular federal income tax liability upon the exercise of the Option,
although the excess, if any, of the Fair Market Value of the Shares on the date
of exercise over the Exercise Price will be treated as an adjustment to the
alternative minimum tax for federal tax purposes and may subject the Optionee to
the alternative minimum tax in the year of exercise.

          (b)  Exercise of ISO Following Disability.  If the Optionee ceases to
               ------------------------------------
be an Employee as a result of a disability that is not a total and permanent
disability as defined in Section 22(e)(3) of the Code, to the extent permitted
on the date of termination, the Optionee must exercise an ISO within three
months of such termination for the ISO to be qualified as an ISO.

          (c)  Exercise of Nonstatutory Stock Option.  There may be a regular
               -------------------------------------
federal income tax liability upon the exercise of a Nonstatutory Stock Option.
The Optionee will be treated as having received compensation income (taxable at
ordinary income tax rates) equal to the excess, if any, of the Fair Market Value
of the Shares on the date of exercise over the Exercise Price. If Optionee is an
Employee or a former Employee, the Company will be required to withhold from
Optionee's compensation or collect from Optionee and pay to the applicable
taxing authorities an amount in cash equal to a percentage of this compensation
income at the time of exercise, and may refuse to honor the exercise and refuse
to deliver Shares if such withholding amounts are not delivered at the time of
exercise.

          (d)  Disposition of Shares.  In the case of an NSO, if Shares are
               ---------------------
held for at least one year, any gain realized on disposition of the Shares will
be treated as long-term capital gain for

                                      -5-
<PAGE>

federal income tax purposes. In the case of an ISO, if Shares transferred
pursuant to the Option are held for at least one year after exercise and at
least two years after the Date of Grant, any gain realized on disposition of the
Shares will also be treated as long-term capital gain for federal income tax
purposes. If Shares purchased under an ISO are disposed of within one year after
exercise or two years after the Date of Grant, any gain realized on such
disposition will be treated as compensation income (taxable at ordinary income
rates) to the extent of the difference between the Exercise Price and the lesser
of (i) the Fair Market Value of the Shares on the date of exercise, or (ii) the
sale price of the Shares. Any additional gain will be taxed as capital gain,
short-term depending on the period that the ISO Shares were held.

          (e)  Notice of Disqualifying Disposition of ISO Shares.  If the
               -------------------------------------------------
Option granted to Optionee herein is an ISO, and if Optionee sells or otherwise
disposes of any of the Shares acquired pursuant to the ISO on or before the
later of (i) the date two years after the Date of Grant, or (ii) the date one
year after the date of exercise, the Optionee shall immediately notify the
Company in writing of such disposition. Optionee agrees that Optionee may be
subject to income tax withholding by the Company on the compensation income
recognized by the Optionee.

          (f)  Section 83(b) Election for Unvested Shares Purchased Pursuant to
               -----------------------------------------------------------------
Options.  With respect to the exercise of an Option for unvested Shares, an
-------
election may be filed by the Optionee with the Internal Revenue Service, within
                                                                         ------
30 days of the purchase of the Shares, electing pursuant to Section 83(b) of the
-------
Code to be taxed currently on any difference between the purchase price of the
Shares and their Fair Market Value on the date of purchase. In the case of a
Nonstatutory Stock Option, this will result in a recognition of taxable income
to the Optionee on the date of exercise, measured by the excess, if any, of the
fair market value of the Shares, at the time the Option is exercised over the
purchase price for the Shares. Absent such an election, taxable income will be
measured and recognized by Optionee at the time or times on which the Company's
Repurchase Option lapses. In the case of an Incentive Stock Option, such an
election will result in a recognition of income to the Optionee for alternative
minimum tax purposes on the date of exercise, measured by the excess, if any, of
the fair market value of the Shares, at the time the option is exercised, over
the purchase price for the Shares. Absent such an election, alternative minimum
taxable income will be measured and recognized by Optionee at the time or times
on which the Company's Repurchase Option lapses. Optionee is strongly encouraged
to seek the advice of his or her own tax consultants in connection with the
purchase of the Shares and the advisability of filing of the Election under
Section 83(b) of the Code. A form of Election under Section 83(b) is attached
hereto as Exhibit E-5 for reference.
          -----------

     OPTIONEE ACKNOWLEDGES THAT IT IS OPTIONEE'S SOLE RESPONSIBILITY AND NOT THE
COMPANY'S TO FILE TIMELY THE ELECTION UNDER SECTION 83(b), EVEN IF OPTIONEE
REQUESTS THE COMPANY OR ITS REPRESENTATIVE TO MAKE THIS FILING ON OPTIONEE'S
BEHALF.

                                      -6-
<PAGE>

     10.  Entire Agreement; Governing Law.  The Plan is incorporated herein by
          -------------------------------
reference.  The Plan and this Option Agreement constitute the entire agreement
of the parties with respect to the subject matter hereof and supersede in their
entirety all prior undertakings and agreements of the Company and Optionee with
respect to the subject matter hereof, and may not be modified adversely to the
Optionee's interest except by means of a writing signed by the Company and
Optionee.  This agreement is governed by the internal substantive laws but not
the choice of law rules of California.

     11.  No Guarantee of Continued Service.  OPTIONEE ACKNOWLEDGES AND AGREES
          ---------------------------------
THAT THE VESTING OF SHARES PURSUANT TO THE VESTING SCHEDULE HEREOF IS EARNED
ONLY BY CONTINUING AS A SERVICE PROVIDER AT THE WILL OF THE COMPANY (NOT THROUGH
THE ACT OF BEING HIRED, BEING GRANTED THIS OPTION OR ACQUIRING SHARES
HEREUNDER). OPTIONEE FURTHER ACKNOWLEDGES AND AGREES THAT THIS AGREEMENT, THE
TRANSACTIONS CONTEMPLATED HEREUNDER AND THE VESTING SCHEDULE SET FORTH HEREIN DO
NOT CONSTITUTE AN EXPRESS OR IMPLIED PROMISE OF CONTINUED ENGAGEMENT AS A
SERVICE PROVIDER FOR THE VESTING PERIOD, FOR ANY PERIOD, OR AT ALL, AND SHALL
NOT INTERFERE IN ANY WAY WITH OPTIONEE'S RIGHT OR THE COMPANY'S RIGHT TO
TERMINATE OPTIONEE'S RELATIONSHIP AS A SERVICE PROVIDER AT ANY TIME, WITH OR
WITHOUT CAUSE.

     Optionee acknowledges receipt of a copy of the Plan and represents that he
or she is familiar with the terms and provisions thereof, and hereby accepts
this Option subject to all of the terms and provisions thereof.  Optionee has
reviewed the Plan and this Option in their entirety, has had an opportunity to
obtain the advice of counsel prior to executing this Option and fully
understands all provisions of the Option.  Optionee hereby agrees to accept as
binding, conclusive and final all decisions or interpretations of the
Administrator upon any questions arising under the Plan or this Option.
Optionee further agrees to notify the Company upon any change in the residence
address indicated below.


OPTIONEE:                          NUMERICAL TECHNOLOGIES, INC.

/s/ Yao-Ting Wang                  /s/ Yagyensh C. Pati
------------------------------     --------------------------------------
Signature                          By


Yao-Ting Wang                      President & CEO
------------------------------     ______________________________________
Print Name                         Title


970 Corte Madera Avenue, #311
------------------------------
Sunnyvale, CA  94086
------------------------------
Residence Address
<PAGE>

                                   EXHIBIT A
                                   ---------

                                2000 STOCK PLAN

                                EXERCISE NOTICE

Numerical Technologies, Inc.
70 West Plumeria Drive
San Jose, CA  95134-2134

Attention:  Secretary

     1.   Exercise of Option.  Effective as of today, February 10, 2000, the
          ------------------
undersigned ("Optionee") hereby elects to exercise Optionee's option to purchase
333,333 shares of the Common Stock (the "Shares") of Numerical Technologies,
Inc. (the "Company") under and pursuant to the 2000 Stock Plan (the "Plan") and
the [ ] Incentive [X] Nonstatutory Stock Option Agreement dated February 1, 2000
(the "Option Agreement").

     2.   Delivery of Payment.  Purchaser herewith delivers to the Company the
          -------------------
full purchase price of the Shares, as set forth in the Option Agreement.

     3.   Representations of Optionee.  Optionee acknowledges that Optionee has
          ---------------------------
received, read and understood the Plan and the Option Agreement and agrees to
abide by and be bound by their terms and conditions.

     4.   Rights as Shareholder.  Until the issuance of the Shares (as evidenced
          ---------------------
by the appropriate entry on the books of the Company or of a duly authorized
transfer agent of the Company), no right to vote or receive dividends or any
other rights as a shareholder shall exist with respect to the Optioned Stock,
notwithstanding the exercise of the Option. The Shares shall be issued to the
Optionee as soon as practicable after the Option is exercised. No adjustment
shall be made for a dividend or other right for which the record date is prior
to the date of issuance except as provided in Section 14 of the Plan.

     5.   Company's Right of First Refusal.  Before any Shares held by Optionee
          --------------------------------
or any transferee (either being sometimes referred to herein as the "Holder")
may be sold or otherwise transferred (including transfer by gift or operation of
law), the Company or its assignee(s) shall have a right of first refusal to
purchase the Shares on the terms and conditions set forth in this Section (the
"Right of First Refusal").

          (a)  Notice of Proposed Transfer.  The Holder of the Shares shall
               ---------------------------
deliver to the Company a written notice (the "Notice") stating: (i) the Holder's
bona fide intention to sell or otherwise transfer such Shares; (ii) the name of
each proposed purchaser or other transferee ("Proposed Transferee"); (iii) the
number of Shares to be transferred to each Proposed Transferee; and (iv) the
bona fide cash price or other consideration for which the Holder proposes to
transfer the Shares (the "Offered Price"), and the Holder shall offer the Shares
at the Offered Price to the Company or its assignee(s).
<PAGE>

          (b)  Exercise of Right of First Refusal.  At any time within thirty
               ----------------------------------
(30) days after receipt of the Notice, the Company and/or its assignee(s) may,
by giving written notice to the Holder, elect to purchase all, but not less than
all, of the Shares proposed to be transferred to any one or more of the Proposed
Transferees, at the purchase price determined in accordance with subsection (c)
below.

          (c)  Purchase Price.  The purchase price ("Purchase Price") for the
               --------------
Shares purchased by the Company or its assignee(s) under this Section shall be
the Offered Price. If the Offered Price includes consideration other than cash,
the cash equivalent value of the non-cash consideration shall be determined by
the Board of Directors of the Company in good faith.

          (d)  Payment.  Payment of the Purchase Price shall be made, at the
               -------
option of the Company or its assignee(s), in cash (by check), by cancellation of
all or a portion of any outstanding indebtedness of the Holder to the Company
(or, in the case of repurchase by an assignee, to the assignee), or by any
combination thereof within 30 days after receipt of the Notice or in the manner
and at the times set forth in the Notice.

          (e)  Holder's Right to Transfer.  If all of the Shares proposed in
               --------------------------
the Notice to be transferred to a given Proposed Transferee are not purchased by
the Company and/or its assignee(s) as provided in this Section, then the Holder
may sell or otherwise transfer such Shares to that Proposed Transferee at the
Offered Price or at a higher price, provided that such sale or other transfer is
consummated within 120 days after the date of the Notice, that any such sale or
other transfer is effected in accordance with any applicable securities laws and
that the Proposed Transferee agrees in writing that the provisions of this
Section shall continue to apply to the Shares in the hands of such Proposed
Transferee. If the Shares described in the Notice are not transferred to the
Proposed Transferee within such period, a new Notice shall be given to the
Company, and the Company and/or its assignees shall again be offered the Right
of First Refusal before any Shares held by the Holder may be sold or otherwise
transferred.

          (f)  Exception for Certain Family Transfers.  Anything to the
               --------------------------------------
contrary contained in this Section notwithstanding, the transfer of any or all
of the Shares during the Optionee's lifetime or on the Optionee's death by will
or intestacy to the Optionee's immediate family or a trust for the benefit of
the Optionee's immediate family shall be exempt from the provisions of this
Section. "Immediate Family" as used herein shall mean spouse, lineal descendant
or antecedent, father, mother, brother or sister. In such case, the transferee
or other recipient shall receive and hold the Shares so transferred subject to
the provisions of this Section, and there shall be no further transfer of such
Shares except in accordance with the terms of this Section.

          (g)  Termination of Right of First Refusal.  The Right of First
               -------------------------------------
Refusal shall terminate as to any Shares upon the first sale of Common Stock of
the Company to the general public pursuant to a registration statement filed
with and declared effective by the Securities and Exchange Commission under the
Securities Act of 1933, as amended.

     6.   Tax Consultation.  Optionee understands that Optionee may suffer
          ----------------
adverse tax consequences as a result of Optionee's purchase or disposition of
the Shares. Optionee represents that Optionee has consulted with any tax
consultants Optionee deems advisable in connection with

                                      -2-
<PAGE>

the purchase or disposition of the Shares and that Optionee is not relying on
the Company for any tax advice.

     7.   Restrictive Legends and Stop-Transfer Orders.
          --------------------------------------------

          (a)  Legends.  Optionee understands and agrees that the Company shall
               -------
cause the legends set forth below or legends substantially equivalent thereto,
to be placed upon any certificate(s) evidencing ownership of the Shares together
with any other legends that may be required by the Company or by state or
federal securities laws:

          THE SECURITIES REPRESENTED HEREBY HAVE NOT BEEN
          REGISTERED UNDER THE SECURITIES ACT OF 1933 (THE
          "ACT") AND MAY NOT BE OFFERED, SOLD OR OTHERWISE
          TRANSFERRED, PLEDGED OR HYPOTHECATED UNLESS AND
          UNTIL REGISTERED UNDER THE ACT OR, IN THE OPINION
          OF COMPANY COUNSEL SATISFACTORY TO THE ISSUER OF
          THESE SECURITIES, SUCH OFFER, SALE OR TRANSFER,
          PLEDGE OR HYPOTHECATION IS IN COMPLIANCE
          THEREWITH.

          THE SHARES REPRESENTED BY THIS CERTIFICATE ARE
          SUBJECT TO CERTAIN RESTRICTIONS ON TRANSFER AND
          RIGHT OF FIRST REFUSAL OPTIONS HELD BY THE ISSUER
          OR ITS ASSIGNEE(S) AS SET FORTH IN THE EXERCISE
          NOTICE BETWEEN THE ISSUER AND THE ORIGINAL HOLDER
          OF THESE SHARES, A COPY OF WHICH MAY BE OBTAINED
          AT THE PRINCIPAL OFFICE OF THE ISSUER. SUCH
          TRANSFER RESTRICTIONS AND RIGHT OF FIRST REFUSAL
          ARE BINDING ON TRANSFEREES OF THESE SHARES.

          (b)  Stop-Transfer Notices.  Optionee agrees that, in order to ensure
               ---------------------
compliance with the restrictions referred to herein, the Company may issue
appropriate "stop transfer" instructions to its transfer agent, if any, and
that, if the Company transfers its own securities, it may make appropriate
notations to the same effect in its own records.

          (c)  Refusal to Transfer.  The Company shall not be required (i) to
               -------------------
transfer on its books any Shares that have been sold or otherwise transferred in
violation of any of the provisions of this Agreement or (ii) to treat as owner
of such Shares or to accord the right to vote or pay dividends to any purchaser
or other transferee to whom such Shares shall have been so transferred.

     8.   Successors and Assigns.  The Company may assign any of its rights
          ----------------------
under this Agreement to single or multiple assignees, and this Agreement shall
inure to the benefit of the successors and assigns of the Company. Subject to
the restrictions on transfer herein set forth, this Agreement shall be binding
upon Optionee and his or her heirs, executors, administrators, successors and
assigns.

                                      -3-
<PAGE>

     9.   Interpretation.  Any dispute regarding the interpretation of this
          --------------
Agreement shall be submitted by Optionee or by the Company forthwith to the
Administrator which shall review such dispute at its next regular meeting. The
resolution of such a dispute by the Administrator shall be final and binding on
all parties.

     10.  Governing Law; Severability.  This Agreement is governed by the
          ---------------------------
internal substantive laws, but not the choice of law rules, of California.

     11.  Entire Agreement.  The Plan and Option Agreement are incorporated
          ----------------
herein by reference. This Agreement, the Plan, the Restricted Stock Purchase
Agreement, the Option Agreement and the Investment Representation Statement
constitute the entire agreement of the parties with respect to the subject
matter hereof and supersede in their entirety all prior undertakings and
agreements of the Company and Optionee with respect to the subject matter
hereof, and may not be modified adversely to the Optionee's interest except by
means of a writing signed by the Company and Optionee.

Submitted by:                      Accepted by:

OPTIONEE:                          NUMERICAL TECHNOLOGIES, INC.

/s/ Yao-Ting Wang                  /s/ Yagyensh C. Pati
_______________________________    _____________________________________________
Signature                          By


Yao-Ting Wang                      President & CEO
-------------------------------    _____________________________________________
Print Name                         Its


Address:                           Address:
-------                            -------

970 Corte Madera Avenue, #311      70 West Plumeria Drive
-------------------------------
                                   San Jose, CA 95134-2134
Sunnyvale, CA  94086
-------------------------------

_______________________________

                                   February 10, 2000
                                   ---------------------------------------------
                                   Date Received
<PAGE>

                                   EXHIBIT B
                                   ---------

               INVESTMENT REPRESENTATION STATEMENT

OPTIONEE :     YAO-TING WANG

COMPANY  :     NUMERICAL TECHNOLOGIES, INC.

SECURITY :     COMMON STOCK

AMOUNT   :     333,333 SHARES

DATE     :     FEBRUARY 10, 2000

     In connection with the purchase of the above-listed Securities, the
undersigned Optionee represents to the Company the following:

          (a)  Optionee is aware of the Company's business affairs and financial
condition and has acquired sufficient information about the Company to reach an
informed and knowledgeable decision to acquire the Securities. Optionee is
acquiring these Securities for investment for Optionee's own account only and
not with a view to, or for resale in connection with, any "distribution" thereof
within the meaning of the Securities Act of 1933, as amended (the "Securities
Act").

          (b)  Optionee acknowledges and understands that the Securities
constitute "restricted securities" under the Securities Act and have not been
registered under the Securities Act in reliance upon a specific exemption
therefrom, which exemption depends upon, among other things, the bona fide
nature of Optionee's investment intent as expressed herein. In this connection,
Optionee understands that, in the view of the Securities and Exchange
Commission, the statutory basis for such exemption may be unavailable if
Optionee's representation was predicated solely upon a present intention to hold
these Securities for the minimum capital gains period specified under tax
statutes, for a deferred sale, for or until an increase or decrease in the
market price of the Securities, or for a period of one year or any other fixed
period in the future. Optionee further understands that the Securities must be
held indefinitely unless they are subsequently registered under the Securities
Act or an exemption from such registration is available. Except as set forth in
the 1999 Second Amended and Restated Shareholder Rights Agreement dated January
1, 2000, as amended January 14, 2000, Optionee further acknowledges and
understands that the Company is under no obligation to register the Securities.
Optionee understands that the certificate evidencing the Securities will be
imprinted with a legend which prohibits the transfer of the Securities unless
they are registered or such registration is not required in the opinion of
counsel satisfactory to the Company, and any other legend required under
applicable state securities laws.

          (c)  Optionee is familiar with the provisions of Rule 144, promulgated
under the Securities Act, which, in substance, permits limited public resale of
"restricted securities" acquired, directly or indirectly, from the issuer
thereof (or from an affiliate of such issuer), in a non-public offering subject
to the satisfaction of certain conditions, including, among other things: (1)
the
<PAGE>

resale occurring not less than one year after the later of the date the
securities were sold by the Company or the date they were sold by an affiliate
of the Company, within the meaning of Rule 144; and, in the case of an
affiliate, or of a non-affiliate who has held the securities less than two
years, (2) the availability of certain public information about the Company, (3)
the sale being made through a broker in an unsolicited "broker's transaction" or
in transactions directly with a market maker (as said term is defined under the
Securities Exchange Act of 1934), and (4) the amount of securities being sold
during any three month period not exceeding the specified limitations stated
therein, if applicable.

          (d)  Optionee further understands that in the event all of the
applicable requirements of or 144 are not satisfied, registration under the
Securities Act, compliance with Regulation A, or some other registration
exemption will be required; and that, notwithstanding the fact that Rule 144 is
not exclusive, the Staff of the Securities and Exchange Commission has expressed
its opinion that persons proposing to sell private placement securities other
than in a registered offering and otherwise than pursuant to Rule 144 will have
a substantial burden of proof in establishing that an exemption from
registration is available for such offers or sales, and that such persons and
their respective brokers who participate in such transactions do so at their own
risk. Optionee understands that no assurances can be given that any such other
registration exemption will be available in such event.


                                   Signature of Optionee:

                                   /s/ Yao-Ting Wang
                                   ___________________________________

                                   Date:  February 10, 2000
<PAGE>

                                   EXHIBIT C
                                   ---------

                              SECURITY AGREEMENT

     This Security Agreement is made as of February 10, 2000 between Numerical
Technologies, Inc., a California corporation ("Pledgee"), and Yao-Ting Wang
("Pledgor").

                                   Recitals
                                   --------

     Pursuant to Pledgor's election to purchase Shares under the Option
Agreement dated February 1, 2000 (the "Option"), between Pledgor and Pledgee
under Pledgee's 2000 Stock Plan, and Pledgor's election under the terms of the
Option to pay for such shares with his promissory note (the "Note"), Pledgor has
purchased 333,333 shares of Pledgee's Common Stock (the "Shares") at a price of
$4.00 per share, for a total purchase price of $1,333,332.00.  The Note and the
obligations thereunder are as set forth in Exhibit D to the Option.

     NOW, THEREFORE, it is agreed as follows:

     A.   Creation and Description of Security Interest. In consideration of the
          ---------------------------------------------
transfer of the Shares to Pledgor under the Option Agreement, Pledgor, pursuant
to the California Commercial Code, hereby pledges all of such Shares (herein
sometimes referred to as the "Collateral") represented by certificate number
242, duly endorsed in blank or with executed stock powers, and herewith delivers
said certificate to the Secretary of Pledgee ("Pledgeholder"), who shall hold
said certificate subject to the terms and conditions of this Security Agreement.

     The pledged stock (together with an executed blank stock assignment for use
in transferring all or a portion of the Shares to Pledgee if, as and when
required pursuant to this Security Agreement) shall be held by the Pledgeholder
as security for the repayment of the Note, and any extensions or renewals
thereof, to be executed by Pledgor pursuant to the terms of the Option, and the
Pledgeholder shall not encumber or dispose of such Shares except in accordance
with the provisions of this Security Agreement.

     B.   Pledgor's Representations and Covenants.  To induce Pledgee to enter
          ---------------------------------------
into this Security Agreement, Pledgor represents and covenants to Pledgee, its
successors and assigns, as follows:

          (A) Payment of Indebtedness.  Pledgor will pay the principal sum of
              -----------------------
the Note secured hereby, together with interest thereon, at the time and in the
manner provided in the Note.

          (B) Encumbrances.  The Shares are free of all other encumbrances,
              ------------
defenses and liens, and Pledgor will not further encumber the Shares without the
prior written consent of Pledgee.

          (C) Margin Regulations.  In the event that Pledgee's Common Stock is
              ------------------
now or later becomes margin-listed by the Federal Reserve Board and Pledgee is
                                          -------
classified as a "lender" within the meaning of the regulations under Part 207 of
Title 12 of the Code of Federal Regulations
<PAGE>

("Regulation G"), Pledgor agrees to cooperate with Pledgee in making any
amendments to the Note or providing any additional collateral as may be
necessary to comply with such regulations.

     C.  Voting Rights.  During the term of this pledge and so long as all
         -------------
payments of principal and interest are made as they become due under the terms
of the Note, Pledgor shall have the right to vote all of the Shares pledged
hereunder.

     D.  Stock Adjustments.  In the event that during the term of the pledge any
         -----------------
stock dividend, reclassification, readjustment or other changes are declared or
made in the capital structure of Pledgee, all new, substituted and additional
shares or other securities issued by reason of any such change shall be
delivered to and held by the Pledgee under the terms of this Security Agreement
in the same manner as the Shares originally pledged hereunder.  In the event of
substitution of such securities, Pledgor, Pledgee and Pledgeholder shall
cooperate and execute such documents as are reasonable so as to provide for the
substitution of such Collateral and, upon such substitution, references to
"Shares" in this Security Agreement shall include the substituted shares of
capital stock of Pledgor as a result thereof.

     E.  Options and Rights.  In the event that, during the term of this pledge,
         ------------------
subscription Options or other rights or options shall be issued in connection
with the pledged Shares, such rights, Options and options shall be the property
of Pledgor and, if exercised by Pledgor, all new stock or other securities so
acquired by Pledgor as it relates to the pledged Shares then held by
Pledgeholder shall be immediately delivered to Pledgeholder, to be held under
the terms of this Security Agreement in the same manner as the Shares pledged.

     F  Default.  Pledgor shall be deemed to be in default of the Note and of
        -------
this Security Agreement in the event:

        (A) Payment of principal or interest on the Note shall be delinquent for
a period of 10 days or more; or

        (B) Pledgor fails to perform any of the covenants set forth in the
Option or contained in this Security Agreement for a period of 10 days after
written notice thereof from Pledgee.

     In the case of an event of Default, as set forth above, Pledgee shall have
the right to accelerate payment of the Note upon notice to Pledgor, and Pledgee
shall thereafter be entitled to pursue its remedies under the California
Commercial Code.

     (G) Release of Collateral.  Subject to any applicable contrary rules under
         ---------------------
Regulation G, there shall be released from this pledge a portion of the pledged
Shares held by Pledgeholder hereunder upon payments of the principal of the
Note.  The number of the pledged Shares which shall be released shall be that
number of full Shares which bears the same proportion to the initial number of
Shares pledged hereunder as the payment of principal bears to the initial full
principal amount of the Note.

                                      -2-
<PAGE>

     (H) Withdrawal or Substitution of Collateral.  Pledgor shall not sell,
         ----------------------------------------
withdraw, pledge, substitute or otherwise dispose of all or any part of the
Collateral without the prior written consent of Pledgee.

     (I) Term.  The within pledge of Shares shall continue until the payment of
         ----
all indebtedness secured hereby, at which time the remaining pledged stock shall
be promptly delivered to Pledgor, subject to the provisions for prior release of
a portion of the Collateral as provided in paragraph 7 above.

     (J) Insolvency.  Pledgor agrees that if a bankruptcy or insolvency
         ----------
proceeding is instituted by or against it, or if a receiver is appointed for the
property of Pledgor, or if Pledgor makes an assignment for the benefit of
creditors, the entire amount unpaid on the Note shall become immediately due and
payable, and Pledgee may proceed as provided in the case of default.

     (K) Pledgeholder Liability.  In the absence of willful or gross negligence,
         ----------------------
Pledgeholder shall not be liable to any party for any of his acts, or omissions
to act, as Pledgeholder.

     (L) Invalidity of Particular Provisions.  Pledgor and Pledgee agree that
         -----------------------------------
the enforceability or invalidity of any provision or provisions of this Security
Agreement shall not render any other provision or provisions herein contained
unenforceable or invalid.

     (M) Successors or Assigns.  Pledgor and Pledgee agree that all of the terms
         ---------------------
of this Security Agreement shall be binding on their respective successors and
assigns, and that the term "Pledgor" and the term "Pledgee" as used herein shall
be deemed to include, for all purposes, the respective designees, successors,
assigns, heirs, executors and administrators.

     (N) Governing Law.  This Security Agreement shall be interpreted and
         -------------
governed under the internal substantive laws, but not the choice of law rules,
of California.

                                      -3-
<PAGE>

     IN WITNESS WHEREOF, the parties hereto have executed this Agreement as of
the day and year first above written.

                                       /s/ Yao-Ting Wang
     "PLEDGOR"                         _____________________________________
                                       Signature

                                       Yao-Ting Wang
                                       --------------------------------------
                                       Print Name

                                                970 Corte Madera Avenue, #311
                                       Address: _____________________________

                                                Sunnyvale, CA 94086
                                                _____________________________


     "PLEDGEE"                         NUMERICAL TECHNOLOGIES, INC.
                                       a California corporation

                                       /s/ Yagyensh C. Pati
                                       __________________________________
                                       Signature

                                       Yagyensh C. Pati
                                       __________________________________
                                       Print Name

                                       President & CEO
                                       __________________________________
                                       Title

                                       /s/ Yagyensh C. Pati
     "PLEDGEHOLDER"                    __________________________________
                                       Secretary of Numerical Technologies, Inc.
<PAGE>

                                   EXHIBIT D
                                   ---------

                                     NOTE

$1,333,332.00                                            Santa Clara, California

                                                               February 10, 2000


     FOR VALUE RECEIVED, Yao-Ting Wang promises to pay to Numerical
Technologies, Inc., a California corporation (the "Company"), or order, the
principal sum of One Million Three Hundred Thirty-Three Thousand Three Hundred
Thirty-Two Dollars ($1,333,332.00), together with interest on the unpaid
principal hereof from the date hereof at the rate of 6.20% per annum, compounded
annually.

     Principal and interest shall be due and payable on February 10, 2002.
Payment of principal and interest shall be made in lawful money of the United
States of America.

     The undersigned may at any time prepay all or any portion of the principal
or interest owing hereunder.

     This Note is subject to the terms of the Option, dated as of February 1,
2000.  This Note is secured in part by a pledge of the Company's Common Stock
under the terms of a Security Agreement of even date herewith and is subject to
all the provisions thereof.

     The holder of this Note shall have full recourse against the undersigned,
and shall not be required to proceed against the collateral securing this Note
in the event of default.

     In the event the undersigned shall cease to be an employee, director or
consultant of the Company for any reason, this Note shall, at the option of the
Company, be accelerated, and the whole unpaid balance on this Note of principal
and accrued interest shall be immediately due and payable.

     Should any action be instituted for the collection of this Note, the
reasonable costs and attorneys' fees therein of the holder shall be paid by the
undersigned.

                                    /s/ Yao-Ting Wang
                                    ____________________________________
                                    Yao-Ting Wang
<PAGE>

                                  EXHIBIT E-1
                                  -----------

                         NUMERICAL TECHNOLOGIES, INC.

                                2000 STOCK PLAN

                      RESTRICTED STOCK PURCHASE AGREEMENT


     THIS AGREEMENT is made between Yao-Ting Wang (the "Purchaser") and
Numerical Technologies, Inc. (the "Company") as of February 10, 2000.

                                   RECITALS
                                   --------

     (1) Pursuant to the exercise of the stock option granted to Purchaser under
the Company's 2000 Stock Plan (the "Plan") and pursuant to the Stock Option
Agreement (the "Option Agreement") dated February 1, 2000 by and between the
Company and Purchaser with respect to such grant, which Plan and Option
Agreement are hereby incorporated by reference, Purchaser has elected to
purchase 333,333 of those shares which have not become vested under the vesting
schedule set forth in the Option Agreement ("Unvested Shares").  The Unvested
Shares and the shares subject to the Option Agreement which have become vested
are sometimes collectively referred to herein as the "Shares".

     (2) As required by the Option Agreement, as a condition to Purchaser's
election to exercise the option, Purchaser must execute this Restricted Stock
Purchase Agreement, which sets forth the rights and obligations of the parties
with respect to Shares acquired upon exercise of the Option.

     1.  Repurchase Option.
         -----------------
         (a)  If Purchaser's status as a Service Provider is terminated for any
reason, including for cause, death, and disability, the Company shall have the
right and option to purchase from Purchaser, or Purchaser's personal
representative, as the case may be, all of the Purchaser's Unvested Shares as of
the date of such termination at the price paid by the Purchaser for such Shares
(the "Repurchase Option").

         (b)  Upon the occurrence of a termination, the Company may exercise its
Repurchase Option by delivering personally or by registered mail, to Purchaser
(or his transferee or legal representative, as the case may be), within ninety
(90) days of the termination, a notice in writing indicating the Company's
intention to exercise the Repurchase Option and setting forth a date for closing
not later than thirty (30) days from the mailing of such notice. The closing
shall take place at the Company's office. At the closing, the holder of the
certificates for the Unvested Shares being transferred shall deliver the stock
certificate or certificates evidencing the Unvested Shares, and the Company
shall deliver the purchase price therefor.
<PAGE>

         (c)  At its option, the Company may elect to make payment for the
Unvested Shares to a bank selected by the Company. The Company shall avail
itself of this option by a notice in writing to Purchaser stating the name and
address of the bank, date of closing, and waiving the closing at the Company's
office.

         (d)  If the C ompany does not elect to exercise the Repurchase Option
conferred above by giving the requisite notice within ninety (90) days following
the termination, the Repurchase Option shall terminate.

         (e)  The Repurchase Option shall terminate in accordance with the
Vesting Schedule in Optionee's Option Agreement.

     2.  Transferability of the Shares; Escrow.
         -------------------------------------

         (a)  Purchaser hereby authorizes and directs the secretary of the
Company, or such other person designated by the Company, to transfer the
Unvested Shares as to which the Repurchase Option has been exercised from
Purchaser to the Company.

         (b)  To insure the availability for delivery of Purchaser's Unvested
Shares upon repurchase by the Company pursuant to the Repurchase Option under
Section 1, Purchaser hereby appoints the secretary, or any other person
designated by the Company as escrow agent, as its attorney-in-fact to sell,
assign and transfer unto the Company, such Unvested Shares, if any, repurchased
by the Company pursuant to the Repurchase Option and shall, upon execution of
this Agreement, deliver and deposit with the secretary of the Company, or such
other person designated by the Company, the share certificates representing the
Unvested Shares, together with the stock assignment duly endorsed in blank,
attached hereto as Exhibit E-2. The Unvested Shares and stock assignment shall
                   -----------
be held by the secretary in escrow, pursuant to the Joint Escrow Instructions of
the Company and Purchaser attached as Exhibit E-3 hereto, until the Company
                                      -----------
exercises its purchase right as provided in Section 1, until such Unvested
Shares are vested, or until such time as this Agreement no longer is in effect.
As a further condition to the Company's obligations under this Agreement, the
spouse of the Purchaser, if any, shall execute and deliver to the Company the
Consent of Spouse attached hereto as Exhibit E-4. Upon vesting of the Unvested
                                     -----------
Shares, the escrow agent shall promptly deliver to the Purchaser the certificate
or certificates representing such Shares in the escrow agent's possession
belonging to the Purchaser, and the escrow agent shall be discharged of all
further obligations hereunder; provided, however, that the escrow agent shall
nevertheless retain such certificate or certificates as escrow agent if so
required pursuant to other restrictions imposed pursuant to this Agreement.

         (c)  The Company, or its designee, shall not be liable for any act it
may do or omit to do with respect to holding the Shares in escrow and while
acting in good faith and in the exercise of its judgment.

         (d)  Transfer or sale of the Shares is subject to restrictions on
transfer imposed by any applicable state and federal securities laws. Any
transferee shall hold such Shares subject to all the provisions hereof and the
Exercise Notice executed by the Purchaser with respect to any

                                      -2-
<PAGE>

Unvested Shares purchased by Purchaser and shall acknowledge the same by signing
a copy of this Agreement.

     3.  Ownership, Voting Rights, Duties. This Agreement shall not affect in
         --------------------------------
any way the ownership, voting rights or other rights or duties of Purchaser,
except as specifically provided herein.

     4.  Legends.  The share certificate evidencing the Shares issued hereunder
         -------
shall be endorsed with the following legend (in addition to any legend required
under applicable state securities laws):

     THE SHARES REPRESENTED BY THIS CERTIFICATE ARE SUBJECT TO CERTAIN
RESTRICTIONS UPON TRANSFER AND RIGHTS OF REPURCHASE AS SET FORTH IN AN AGREEMENT
BETWEEN THE COMPANY AND THE STOCKHOLDER, A COPY OF WHICH IS ON FILE WITH THE
SECRETARY OF THE COMPANY.

     5.  Adjustment for Stock Split.  All references to the number of Shares
         --------------------------
and the purchase price of the Shares in this Agreement shall be appropriately
adjusted to reflect any stock split, stock dividend or other change in the
Shares which may be made by the Company after the date of this Agreement.

     6.  Notices.  Notices required hereunder shall be given in person or by
         -------
registered mail to the address of Purchaser shown on the records of the Company,
and to the Company at their respective principal executive offices.

     7.  Survival of Terms.  This Agreement shall apply to and bind Purchaser
         -----------------
and the Company and their respective permitted assignees and transferees, heirs,
legatees, executors, administrators and legal successors.

     8.  Section 83(b) Election.  Purchaser hereby acknowledges that he or she
         ----------------------
has been informed that, with respect to the exercise of an Option for unvested
Shares, an election may be filed by the Purchaser with the Internal Revenue
Service, within 30 days of the purchase of the Shares, electing pursuant to
         --------------
Section 83(b) of the Code to be taxed currently on any difference between the
purchase price of the Shares and their Fair Market Value on the date of
purchase.  In the case of a Nonstatutory Stock Option, this will result in a
recognition of taxable income to the Purchaser on the date of exercise, measured
by the excess, if any, of the fair market value of the Shares, at the time the
Option is exercised over the purchase price for the Shares.  Absent such an
election, taxable income will be measured and recognized by Purchaser at the
time or times on which the Company's Repurchase Option lapses.  In the case of
an Incentive Stock Option, such an election will result in a recognition of
income to the Purchaser for alternative minimum tax purposes on the date of
exercise, measured by the excess, if any, of the fair market value of the
Shares, at the time the option is exercised, over the purchase price for the
Shares.  Absent such an election, alternative minimum taxable income will be
measured and recognized by Purchaser at the time or times on which the Company's
Repurchase Option lapses.   Purchaser is strongly encouraged to seek the advice
of his or her own tax consultants in connection with the purchase of the Shares
and the advisability of filing

                                      -3-
<PAGE>

of the Election under Section 83(b) of the Code. A form of Election under
Section 83(b) is attached hereto as Exhibit E-5 for reference.
                                    -----------

     PURCHASER ACKNOWLEDGES THAT IT IS PURCHASER'S SOLE RESPONSIBILITY AND NOT
THE COMPANY'S TO FILE TIMELY THE ELECTION UNDER SECTION 83(b), EVEN IF PURCHASER
REQUESTS THE COMPANY OR ITS REPRESENTATIVE TO MAKE THIS FILING ON PURCHASER'S
BEHALF.

     9.  Representations.  Purchaser has reviewed with his own tax advisors the
         ---------------
federal, state, local and foreign tax consequences of this investment and the
transactions contemplated by this Agreement.  Purchaser is relying solely on
such advisors and not on any statements or representations of the Company or any
of its agents.  Purchaser understands that he (and not the Company) shall be
responsible for his own tax liability that may arise as a result of this
investment or the transactions contemplated by this Agreement.

     10. Governing Law.  This Agreement shall be governed by the internal
         -------------
substantive laws, but not the choice of law rules, of California.

     Purchaser represents that he has read this Agreement and is familiar with
its terms and provisions.  Purchaser hereby agrees to accept as binding,
conclusive and final all decisions or interpretations of the Board upon any
questions arising under this Agreement.

                                      -4-
<PAGE>

     IN WITNESS WHEREOF, this Agreement is deemed made as of the date first set
forth above.

                                    "COMPANY"

                                    NUMERICAL TECHNOLOGIES, INC.

                                    /s/ Yagyensh C. Pati
                                    __________________________________
                                    By

                                    President & CEO
                                    __________________________________
                                    Title

                                    "PURCHASER"

                                    /s/ Yao-Ting Wang
                                    __________________________________
                                    Signature

                                    Yao-Ting Wang
                                    ----------------------------------
                                    Printed Name

                                    ###-##-####
                                    __________________________________
                                    Soc. Sec. No.

                                    Address:
                                    -------

                                    970 Corte Madera Avenue, #311
                                    ----------------------------------

                                    Sunnyvale, CA  94086
                                    -----------------------------------
<PAGE>

                                  EXHIBIT E-2
                                  -----------

                     ASSIGNMENT SEPARATE FROM CERTIFICATE

     FOR VALUE RECEIVED I, __________________________, hereby sell, assign and
transfer unto Numerical Technologies, Inc. (__________) shares of the Common
Stock of Numerical Technologies, Inc. standing in my name of the books of said
corporation represented by Certificate No. _____ herewith and do hereby
irrevocably constitute and appoint _______________________ to transfer the said
stock on the books of the within named corporation with full power of
substitution in the premises.

     This Stock Assignment may be used only in accordance with the Restricted
Stock Purchase Agreement between Numerical Technologies, Inc. and the
undersigned dated ______________, 20___.


Dated: _________________, ____


               /s/ Yao-Ting Wang
     Signature:___________________________________






     INSTRUCTIONS: Please do not fill in any blanks other than the signature
line.  The purpose of this assignment is to enable the Company to exercise its
"repurchase option," as set forth in the Agreement, without requiring additional
signatures on the part of the Purchaser.
<PAGE>

                                  EXHIBIT E-3
                                  -----------

                           JOINT ESCROW INSTRUCTIONS
                           -------------------------

                                                               February 10, 2000

Numerical Technologies, Inc.
70 West Plumeria Drive
San Jose, CA  95134-2134

Attention:  Secretary

Dear ___________:

     As Escrow Agent for both Numerical Technologies, Inc. (the "Company"), and
the undersigned purchaser of stock of the Company (the "Purchaser"), you are
hereby authorized and directed to hold the documents delivered to you pursuant
to the terms of that certain Restricted Stock Purchase Agreement ("Agreement")
between the Company and the undersigned, in accordance with the following
instructions:

     1.  In the event the Company and/or any assignee of the Company (referred
to collectively for convenience herein as the "Company") exercises the Company's
repurchase option set forth in the Agreement, the Company shall give to
Purchaser and you a written notice specifying the number of shares of stock to
be purchased, the purchase price, and the time for a closing hereunder at the
principal office of the Company. Purchaser and the Company hereby irrevocably
authorize and direct you to close the transaction contemplated by such notice in
accordance with the terms of said notice.

     2.  At the closing, you are directed (a) to date the stock assignments
necessary for the transfer in question, (b) to fill in the number of shares
being transferred, and (c) to deliver same, together with the certificate
evidencing the shares of stock to be transferred, to the Company or its
assignee, against the simultaneous delivery to you of the purchase price (by
cash, a check, cancellation of indebtedness, or some combination thereof) for
the number of shares of stock being purchased pursuant to the exercise of the
Company's repurchase option.

     3.  Purchaser irrevocably authorizes the Company to deposit with you any
certificates evidencing shares of stock to be held by you hereunder and any
additions and substitutions to said shares as defined in the Agreement.
Purchaser does hereby irrevocably constitute and appoint you as Purchaser's
attorney-in-fact and agent for the term of this escrow to execute with respect
to such securities all documents necessary or appropriate to make such
securities negotiable and to complete any transaction herein contemplated,
including but not limited to the filing with any applicable state blue sky
authority of any required applications for consent to, or notice of transfer of,
the securities. Subject to the provisions of this paragraph 3, Purchaser shall
exercise all rights and privileges of a stockholder of the Company while the
stock is held by you.
<PAGE>

     4.  Provided the Promissory Note dated February 10, 2000 in the principal
amount of $1,333,332.00 and issued by the Purchaser to the Company (the "Note")
has been paid in full, upon written request of the Purchaser, but no more than
once per calendar year, unless the Company's repurchase option has been
exercised, you will deliver to Purchaser a certificate or certificates
representing so many shares of stock as are not then subject to the Company's
repurchase option. Provided the Note has been paid in full, within 120 days
after cessation of Purchaser's continuous employment by or services to the
Company, or any parent or subsidiary of the Company, you will deliver to
Purchaser a certificate or certificates representing the aggregate number of
shares held or issued pursuant to the Agreement and not purchased by the Company
or its assignees pursuant to exercise of the Company's repurchase option.

     5.  If at the time of termination of this escrow you should have in your
possession any documents, securities, or other property belonging to Purchaser,
you shall deliver all of the same to Purchaser and shall be discharged of all
further obligations hereunder.

     6.  Your duties hereunder may be altered, amended, modified or revoked only
by a writing signed by all of the parties hereto.

     7.  You shall be obligated only for the performance of such duties as are
specifically set forth herein and may rely and shall be protected in relying or
refraining from acting on any instrument reasonably believed by you to be
genuine and to have been signed or presented by the proper party or parties.
You shall not be personally liable for any act you may do or omit to do
hereunder as Escrow Agent or as attorney-in-fact for Purchaser while acting in
good faith, and any act done or omitted by you pursuant to the advice of your
own attorneys shall be conclusive evidence of such good faith.

     8.  You are hereby expressly authorized to disregard any and all warnings
given by any of the parties hereto or by any other person or corporation,
excepting only orders or process of courts of law and are hereby expressly
authorized to comply with and obey orders, judgments or decrees of any court. In
case you obey or comply with any such order, judgment or decree, you shall not
be liable to any of the parties hereto or to any other person, firm or
corporation by reason of such compliance, notwithstanding any such order,
judgment or decree being subsequently reversed, modified, annulled, set aside,
vacated or found to have been entered without jurisdiction.

     9.  You shall not be liable in any respect on account of the identity,
authorities or rights of the parties executing or delivering or purporting to
execute or deliver the Agreement or any documents or papers deposited or called
for hereunder.

     10. You shall not be liable for the outlawing of any rights under the
Statute of Limitations with respect to these Joint Escrow Instructions or any
documents deposited with you.

     11. You shall be entitled to employ such legal counsel and other experts as
you may deem necessary properly to advise you in connection with your
obligations hereunder, may rely upon the advice of such counsel, and may pay
such counsel reasonable compensation therefor.

                                      -2-
<PAGE>

     12.  Your responsibilities as Escrow Agent hereunder shall terminate if you
shall cease to be an officer or agent of the Company or if you shall resign by
written notice to each party.  In the event of any such termination, the Company
shall appoint a successor Escrow Agent.

     13.  If you reasonably require other or further instruments in connection
with these Joint Escrow Instructions or obligations in respect hereto, the
necessary parties hereto shall join in furnishing such instruments.

     14.  It is understood and agreed that should any dispute arise with respect
to the delivery and/or ownership or right of possession of the securities held
by you hereunder, you are authorized and directed to retain in your possession
without liability to anyone all or any part of said securities until such
disputes shall have been settled either by mutual written agreement of the
parties concerned or by a final order, decree or judgment of a court of
competent jurisdiction after the time for appeal has expired and no appeal has
been perfected, but you shall be under no duty whatsoever to institute or defend
any such proceedings.

     15.  Any notice required or permitted hereunder shall be given in writing
and shall be deemed effectively given upon personal delivery or upon deposit in
the United States Post Office, by registered or certified mail with postage and
fees prepaid, addressed to each of the other parties thereunto entitled at the
following addresses or at such other addresses as a party may designate by ten
days' advance written notice to each of the other parties hereto.

          COMPANY:            Numerical Technologies, Inc.
                              70 West Plumeria Drive
                              San Jose, CA  95134-2134
                              Attention:  Secretary

          PURCHASER:          Yao-Ting Wang
                              970 Corte Madera Avenue, #311
                              Sunnyvale, CA  94086

          ESCROW AGENT:       Wilson Sonsini, Goodrich & Rosati
                              650 Page Mill Road
                              Palo Alto, CA  94304

     16.  By signing these Joint Escrow Instructions, you become a party hereto
only for the purpose of said Joint Escrow Instructions; you do not become a
party to the Agreement.

     17.  This instrument shall be binding upon and inure to the benefit of the
parties hereto, and their respective successors and permitted
assigns.

                                      -3-
<PAGE>

     18.  These Joint Escrow Instructions shall be governed by the internal
substantive laws, but not the choice of law rules, of California.

                                    NUMERICAL TECHNOLOGIES, INC.

                                    /s/ Yagyensh C. Pati
                                    ____________________________________
                                    By

                                    President & CEO
                                    ____________________________________
                                    Title


                                    PURCHASER

                                    /s/ Yao-Ting Wang
                                    ____________________________________
                                    Signature

                                    Yao-Ting Wang
                                    ------------------------------------
                                    Typed or Printed Name


                                    ESCROW AGENT

                                    WILSON SONSINI GOODRICH & ROSATI

                                    /s/ John V. Roos
                                    ____________________________________
                                    By

                                    Member
                                    ____________________________________
                                    Title
<PAGE>

                                  EXHIBIT E-4
                                  -----------

                               CONSENT OF SPOUSE
                               -----------------

     I, ____________________, spouse of ___________________, have read and
approve the foregoing Agreement.  In consideration of granting of the right to
my spouse to purchase shares of Numerical Technologies, Inc., as set forth in
the Agreement, I hereby appoint my spouse as my attorney-in-fact in respect to
the exercise of any rights under the Agreement and agree to be bound by the
provisions of the Agreement insofar as I may have any rights in said Agreement
or any shares issued pursuant thereto under the community property laws or
similar laws relating to marital property in effect in the state of our
residence as of the date of the signing of the foregoing Agreement.

Dated: ________________, 2000

                                      N/A
                                      -----------------------------------
<PAGE>

                                  EXHIBIT E-5
                                  -----------

                         ELECTION UNDER SECTION 83(b)
                         ----------------------------
                     OF THE INTERNAL REVENUE CODE OF 1986
                     ------------------------------------

The undersigned taxpayer hereby elects, pursuant to Sections 55 and 83(b) of the
Internal Revenue Code of 1986, as amended, to include in taxpayer's gross income
or alternative minimum taxable income, as the case may be, for the current
taxable year the amount of any compensation taxable to taxpayer in connection
with taxpayer's receipt of the property described below:

1.   The name, address, taxpayer identification number and taxable year of the
undersigned are as follows:

     NAME:                   TAXPAYER:       Yao-Ting Wang       SPOUSE:  N/A

     ADDRESS:      970 Corte Madera Avenue, #311, Sunnyvale, CA 94086

     IDENTIFICATION NO.:     TAXPAYER:       ###-##-####         SPOUSE:  N/A

     TAXABLE YEAR:       2000

2.   The property with respect to which the election is made is described as
follows: 333,333 shares (the "Shares") of the Common Stock of Numerical
Technologies, Inc. (the "Company").

3.   The date on which the property was transferred is: Feb. 10, 2000.

4.   The property is subject to the following restrictions:

     The Shares may not be transferred and are subject to forfeiture under the
     terms of an agreement between the taxpayer and the Company.  These
     restrictions lapse upon the satisfaction of certain conditions contained in
     such agreement.

5.   The fair market value at the time of transfer, determined without regard to
any restriction other than a restriction which by its terms will never lapse, of
such property is:

     $4.00 per share.

6.   The amount (if any) paid for such property is:

     $4.00 per share.

The undersigned has submitted a copy of this statement to the person for whom
the services were performed in connection with the undersigned's receipt of the
above-described property.  The transferee of such property is the person
performing the services in connection with the transfer of said property.

The undersigned understands that the foregoing election may not be revoked
--------------------------------------------------------------------------
except with the consent of the Commissioner.
-------------------------------------------

                              /s/ Yao-Ting Wang
Dated:  Feb. 10, 2000         ______________________________________________
                                   Taxpayer

The undersigned spouse of taxpayer joins in this election.

Dated:                        N/A
                              ----------------------------------------------