<PAGE>   1
                                                                EXHIBIT 10.20

                                 [DIGITAL LOGO]


                               AGREEMENT BETWEEN

                            SIMPLEX SOLUTIONS, INC.

                                      AND

                         DIGITAL EQUIPMENT CORPORATION

                           FOR LICENSING OF CAD TOOLS


License # SEG/CAD-92195-1                              Dated September 21, 1995
<PAGE>   2

Table of Contents

1.0       DEFINITIONS

2.0       TITLE AND LICENSE GRANTS

3.0       LICENSE FEES AND PAYMENTS (CONSIDERATION)

4.0       CONFIDENTIALITY

5.0       UPDATES, TRAINING AND SUPPORT SERVICES

6.0       TECHNOLOGY TRANSFER

7.0       WARRANTIES

8.0       LIMITATION OF LIABILITY

9.0       REMEDIES

10.0      INJUNCTIVE RELIEF

11.0      TERMINATION

12.0      NOTICES

13.0      GENERAL TERMS

APPENDIX A LICENSED SOFTWARE AND DOCUMENTATION

<PAGE>   3

                           SOFTWARE LICENSE AGREEMENT

This Agreement is entered into as of September 21, 1995 (EFFECTIVE DATE) by and
between Digital Semiconductor a business unit of Digital Equipment Corporation,
a Massachusetts Corporation with principle offices at 111 Powdermill Road,
Maynard, Massachusetts 01754-1458 (hereinafter "DIGITAL") and Simplex
Solutions, Inc., a Delaware Corporation with principal offices at 2540 North
First Street, Suite 302, San Jose, CA 95131 ("SIMPLEX").

SIMPLEX desires to acquire an EXCLUSIVE LICENSE, except for Digital
Semiconductor's own internal use, for [*] after which this LICENSE reverts to a
NON-EXCLUSIVE LICENSE, to use, modify, develop and create derivative works of
the LICENSED SOFTWARE in source code and binary format, as defined in Appendix A
in order to create SIMPLEX SOFTWARE, and to market, promote and distribute, in
binary format only, such SIMPLEX SOFTWARE internationally.

DIGITAL desires to grant SIMPLEX such EXCLUSIVE LICENSE, except for Digital
Semiconductor's own internal use, for [*] after which this LICENSE reverts to a
NON-EXCLUSIVE LICENSE to use in source code format, and a limited non-exclusive
right to sublicense in binary format only the LICENSED SOFTWARE, as defined in
Appendix A, as part of SIMPLEX SOFTWARE subject to the terms and conditions
hereinafter set forth.

Therefore, for and in consideration of the mutual covenants expressed herein
and other good and valuable consideration, except which the parties hereby
acknowledge, the parties hereby agree as follows:

1.      ARTICLE 1 - DEFINITIONS

As used in this Agreement, the following terms shall have the following
respective meanings:

        1.1.    CONTRACT YEAR shall mean the twelve month period beginning on
                the first anniversary date of the EFFECTIVE DATE and on each
                anniversary of the EFFECTIVE DATE thereafter. CONTRACT YEARS
                shall be referred to by the calendar year in which such CONTRACT
                YEAR began.

        1.2.    DIGITAL and SIMPLEX are hereafter occasionally referred to as
                "party" or "parties" as indicated by the context.

        1.3.    INTELLECTUAL PROPERTY RIGHTS shall mean any of the following
                rights owned or licensed by DIGITAL with respect to LICENSED
                SOFTWARE as delivered hereunder during the term hereof.

                1.3.1.  All rights, title and interests in all Letters Patent
                        including any reissue, division, continuation or
                        continuation-in-part applications throughout the world
                        now or hereafter filed; and

                1.3.2.  All mask work rights including mask work registration
                        rights, all copyright rights, and all other literary
                        property and author rights whether or not copyrightable;
                        and all rights, title and interests in all copyrights,
                        mask work registrations and copyrighted interests; and

                1.3.3.  All rights, title and interests in all know-how and
                        show-how whether or not protectable by patent,
                        copyright, mask work registration or trade secret.

        1.4.    LICENSED SOFTWARE shall mean DIGITAL's CAD software tools in
                both object code and source code forms, as more particularly
                identified and described in Appendix A hereto and shall also
                include DIGITAL's User Guides and reference manuals listed in
                Appendix A.

        1.5.    EXCLUSIVE LICENSE shall mean a license which permits SIMPLEX to
                use the LICENSED SOFTWARE as licensed, but which does not
                prohibit DIGITAL in any manner from making, using and selling
                LICENSED SOFTWARE and products embodying the LICENSED SOFTWARE
                throughout the world, and which does not prohibit DIGITAL from
                granting non-exclusive rights to third parties to use



*Certain information on this page has been omitted and filed separately with
 the Commission. Confidential treatment has been requested with respect to the
 omitted portions.
<PAGE>   4
          LICENSED SOFTWARE for any purpose throughout the world, except for the
          first four (4) years of this LICENSE, for which time Digital shall not
          license any other third party.
          1.5.1.    The term "use" as employed in Article 1.4 above shall
                    include but not be limited to the rights to design,
                    implement, develop, copy, reproduce, manufacture, package,
                    install, operate, test, correct, maintain, repair, enhance,
                    extend, translate, transliterate, and create or sublicense
                    other derivative works.
     1.6. SIMPLEX SOFTWARE shall mean SIMPLEX's [*] (which will incorporate the
          LICENSED SOFTWARE) and [*] (which will not incorporate the LICENSED
          SOFTWARE) software programs as well as any other software owned or
          marketing by SIMPLEX which may incorporate LICENSED SOFTWARE,
          including any manuals and related documentation.
     1.7. TERM shall mean the term of this Agreement commencing on the EFFECTIVE
          DATE and continuing thereafter for a term of [*] years or until
          otherwise terminated in accordance with Article 10 below. Prior to the
          end of the TERM of this Agreement the parties shall confer and
          negotiate in good faith any extension of this Agreement.
     1.8. USE SUBLICENSE shall mean any agreement or arrangement between SIMPLEX
          and any of its end user customers for the lease, license or use of
          SIMPLEX SOFTWARE. USE SUBLICENSES shall only grant end users the right
          to use the SIMPLEX SOFTWARE in binary format.
     1.9. References to an Article in this Agreement shall be deemed to include
          all Articles numerically depending therefrom. For example, a reference
          to Article 2.2 shall be deemed to include Articles 2.2.1 and 2.2.2,
          and a reference to Article 3 shall be deemed to include Article 3.1.

2.   ARTICLE 2 - TITLE AND LICENSE GRANTS
     2.1. Subject to the limited EXCLUSIVE LICENSE granted to SIMPLEX as
          expressly set forth in this Article 2, DIGITAL Owns and shall retain
          all rights, title and interests including INTELLECTUAL PROPERTY RIGHTS
          in the LICENSED SOFTWARE. SIMPLEX shall retain ownership of all
          corrections, adaptations, enhancements and extensions to the SIMPLEX
          SOFTWARE, as well as any derivative works created from the LICENSED
          SOFTWARE, developed by or for SIMPLEX pursuant to the rights licensed
          hereunder.
     2.2. DIGITAL agrees to grant and hereby grants to SIMPLEX under DIGITAL's
          INTELLECTUAL PROPERTY RIGHTS, and subject to the terms of Article 4
          below, a perpetual, irrevocable, worldwide EXCLUSIVE LICENSE, except
          for Digital Semiconductor's own internal use, to use, reproduce,
          develop, modify and create derivative works of the LICENSED SOFTWARE
          in order to create SIMPLEX SOFTWARE, and to use, reproduce,
          distribute, perform and display the SIMPLEX SOFTWARE in binary code
          format only pursuant to the USE SUBLICENSES with the right to further
          sublicense in binary format only to any tier as may be necessary to
          distribute SIMPLEX SOFTWARE to end user customers.
          2.2.1.    SIMPLEX shall label all SIMPLEX SOFTWARE which includes
                    LICENSED SOFTWARE in whole or in part with the following
                    notice: "Portions of this product incorporates technology
                    licensed from Digital Equipment Corporation".
          2.2.2.    In addition to the foregoing, SIMPLEX shall have the right
                    to transfer possession of the source code of the LICENSED
                    SOFTWARE as incorporated in the SIMPLEX SOFTWARE as part of
                    a source code escrow of the SIMPLEX SOFTWARE established for
                    the benefit of end user customers to allow such end users to
                    use such software solely to support and maintain SIMPLEX
                    SOFTWARE in their possession in the event SIMPLEX is unable
                    to do so, in each case subject to escrow terms



*Certain information on this page has been omitted and filed separately with
 the Commission. Confidential treatment has been requested with respect to the
 omitted portions.

                                                                               2
<PAGE>   5

            approved by DIGITAL, which approval may not be unreasonably
            withheld, and confidentiality restrictions and restrictions on use
            of the LICENSED SOFTWARE at least as restrictive as those contained
            in this Agreement. Except for above, SIMPLEX shall have no right to
            distribute the source code of the LICENSED SOFTWARE to any third
            parties.

   2.3. SIMPLEX hereby grants to DIGITAL for its internal purposes only, a fully
        paid, irrevocable, non-exclusive, perpetual, license to use within
        Digital Semiconductor business unit worldwide, under SIMPLEX's
        INTELLECTUAL PROPERTY RIGHTS including patent, copyright, mask work and
        trade secret rights, no more than [*] copies of Simplex's [*] software
        products in executable code form and including documentation. For
        purposes of clarification, DIGITAL may request up to [*] copies of any
        combination of [*]. Each copy may be used only on a single
        workstation/CPU. For SIMPLEX SOFTWARE upgrades which included DIGITAL's
        LICENSED SOFTWARE [*], Digital will receive such upgrades at no charge
        for a period of [*] years from the effective date of this agreement. For
        SIMPLEX SOFTWARE upgrades that do not include DIGITAL's LICENSED
        SOFTWARE [*], Digital xxxxxxxxxxxx at SIMPLEX's prevailing prices. For
        the purposes of this subsection, an "upgrade" is an optional module that
        may be added to a base software product to provide additional
        functionality or performance. Digital will receive maintenance/support
        for the SIMPLEX SOFTWARE through a single DIGITAL support coordinator at
        DIGITAL's Hudson facility for a period of [*] years from the effective
        date of this agreement at no additional charge.

        2.3.1. It is understood by the parties that the license grant to DIGITAL
               under this Article 2.3 shall permit DIGITAL to design, distribute
               and use the SIMPLEX SOFTWARE internally. But, unless otherwise
               agreed by the parties in writing, DIGITAL shall have no right to
               distribute, sublicense or grant access to the SIMPLEX SOFTWARE to
               any third party.

   2.4. DIGITAL and SIMPLEX agree that Articles 2.1 and 2.3 shall survive the
        termination of this Agreement for any reason whatsoever including
        expiration of TERM.

3. ARTICLE 3 - FEES AND ROYALTIES

   3.1. In consideration for DIGITAL's performance under this Agreement, and the
        rights and licenses granted to SIMPLEX under this Agreement, SIMPLEX
        shall grant Digital the licenses defined in Section 2.3 above. SIMPLEX
        [*] any royalty payments.

   3.2. Within four weeks of the execution of this Agreement, DIGITAL shall
        deliver to SIMPLEX one DIGITAL Alpha workstation and related software
        configured as previously specified by SIMPLEX which may be used by
        SIMPLEX for developmental purposes. Such workstation and software shall
        be subject to a separate AGREEMENT FOR LOAN OF PRODUCTS between the
        parties.

4. ARTICLE 4 - CONFIDENTIALITY

   4.1. As used in this Agreement, the term "CONFIDENTIAL INFORMATION" shall
        mean any information disclosed by one party to the other pursuant to
        this Agreement which is in written, graphic, machine readable or other
        tangible form and is marked with the identity of the disclosing party
        and "Confidential", "Proprietary" or in some other manner to indicate
        its confidential nature. CONFIDENTIAL INFORMATION may also include oral
        information disclosed by one party to the other pursuant to this
        Agreement, provided that such information is designated as confidential
        at the time of disclosure and reduced to a written summary by the
        disclosing party, within thirty (30) days after its oral disclosure,
        which is marked in a manner indicated above in Section 4.1 and delivered
        to the receiving party. Notwithstanding any failure to so identify it,
        however, the source



*Certain information on this page has been omitted and filed separately with
 the Commission. Confidential treatment has been requested with respect to the
 omitted portions.
<PAGE>   6

        code for the LICENSED SOFTWARE and the SIMPLEX SOFTWARE shall be deemed
        to be "CONFIDENTIAL INFORMATION" hereunder.

4.2.    Each party shall treat as confidential all CONFIDENTIAL INFORMATION of
        the other party, shall not use such CONFIDENTIAL INFORMATION except as
        expressly set forth herein or otherwise authorized in writing, shall
        implement reasonable procedures to prohibit the disclosure, unauthorized
        duplication, misuse or removal of the other party's CONFIDENTIAL
        INFORMATION and shall not disclose such CONFIDENTIAL INFORMATION to any
        third party except as may be necessary and required in connection with
        the rights and obligations of such party under this Agreement, and
        subject to confidentiality obligations at least as protective as those
        set forth herein. Without limiting the foregoing each of the parties
        shall use at least the same procedures and degree of care which it uses
        to prevent the disclosure of its own CONFIDENTIAL INFORMATION of like
        importance to prevent the disclosure of CONFIDENTIAL INFORMATION
        disclosed to it by the other party under this Agreement, but in no event
        less than reasonable care.

4.3.    The TERM of this Agreement, and for [*] years thereafter SIMPLEX shall
        maintain in confidence and not use except as expressly authorized
        herein, all LICENSED SOFTWARE and derivative works thereof made by
        SIMPLEX that either directly or indirectly discloses LICENSED SOFTWARE.
        ALL LICENSED SOFTWARE shall be referred to hereafter as "CONFIDENTIAL
        INFORMATION".

4.4.    SIMPLEX agrees that the confidentiality of the LICENSED SOFTWARE is an
        integral part of the ascribed value of the LICENSED SOFTWARE.

4.5.    CONFIDENTIAL INFORMATION shall not include and SIMPLEX shall not be
        required to protect in confidence any information disclosed to SIMPLEX
        under this Agreement which;

        4.5.1.   was in the receiving party's possession or was know to the
                 receiving party prior to receipt under this Agreement, as
                 evidenced by a signed and dated document created in the normal
                 course of business or other equally probative evidence;

        4.5.2.   is or becomes public knowledge without breach of this Agreement
                 by the receiving party as evidenced by a printed publication or
                 other equally probative evidence;

        4.5.3.   is or becomes available to the receiving party from a source
                 other than the disclosing party without a confidentiality
                 restriction and without a breach of this Agreement; or

        4.5.4.   is developed by the receiving party independent of and without
                 reference to CONFIDENTIAL INFORMATION received under this
                 Agreement.

        4.5.5.   is disclosed with the prior written approval of the disclosing
                 party;

        4.5.6.   is disclosed pursuant to the order or requirement of a court,
                 administrative agency, or other governmental body; provided,
                 that the receiving party shall provide prompt, advanced notice
                 thereof to enable the disclosing party to seek a protective
                 order or otherwise prevent such disclosure.

4.6.    Each party acknowledges that disclosure or use of any CONFIDENTIAL
        INFORMATION by the other party in a manner inconsistent with this
        Agreement will cause the other party irreparable injury which may not be
        adequately compensated by damages. Accordingly, in addition to all other
        remedies that a disclosing party shall have under this Agreement, the
        disclosing party shall have the right to equitable and injunctive relief
        to prevent the unauthorized use or disclosure of CONFIDENTIAL
        INFORMATION, and shall have the right to such damages (including without
        limitation court costs, and reasonable attorney fees awarded by a court
        of final resort and competent jurisdiction) as are occasioned by such
        unauthorized use or disclosure.



*Certain information on this page has been omitted and filed separately with
 the Commission. Confidential treatment has been requested with respect to the
 omitted portions.

                                                                               4


<PAGE>   7

     4.7.  Neither party shall disclose any confidential third party information
           to the other under this Agreement.

5.   ARTICLE 5 -- UPDATES, TRAINING AND SUPPORT SERVICES

     5.1.  DIGITAL agrees that it shall provide SIMPLEX all error corrections,
           updates, and upgrades to the LICENSED SOFTWARE which DIGITAL may, at
           its discretion, develop and make available internally from time to
           time, as to which DIGITAL shall own all rights, title, and interest.
           It is understood by the parties that such product updates are not on
           a scheduled or planned basis and entail no obligation by DIGITAL to
           actually produce any such updates or upgrades to SIMPLEX.

     5.2.  DIGITAL shall provide SIMPLEX Two person (2) week of training (not
           including time spent prior to execution hereof). Time spent via phone
           communication shall count towards the 2 person/week equivalent.
           DIGITAL, may at its discretion, provide training or support at
           another site: if training/support is not at the Hudson facility, the
           hours spend shall be calculated at double the time (i.e., 2 hours at
           other site = 1 hour at Hudson, MA) and all travel and lodging
           expenses for any DIGITAL personnel involved in such other site
           training will be paid by SIMPLEX. If additional training or support
           is required, DIGITAL may, at its discretion, provide additional
           support for a fee of [*] per day per person plus expenses.

6.   ARTICLE 6 -- TECHNOLOGY TRANSFER

     6.1.  DIGITAL shall deliver to SIMPLEX one complete copy of the LICENSED
           SOFTWARE within 2 weeks of the EFFECTIVE DATE of this Agreement.

     6.2.  If the event this Agreement is terminated in accordance with the
           terms of Article 7, SIMPLEX shall return to DIGITAL all whole or
           partial copies of LICENSED SOFTWARE which are in SIMPLEX's
           possession or control, whether direct or indirect.

7.   ARTICLE 7 -- WARRANTY PROVISIONS

     7.1.  THE LICENSED SOFTWARE AND THE SIMPLEX SOFTWARE ARE PROVIDED "AS IS"
           UNDER THIS AGREEMENT. NEITHER PARTY MAKES ANY WARRANTIES UNDER THIS
           AGREEMENT, WHETHER EXPRESS OR IMPLIED, AND SPECIFICALLY DISCLAIMS
           ANY IMPLIED WARRANTY OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
           PURPOSE. THE LICENSED SOFTWARE IS DEVELOPED FOR INTERNAL USE, AND IS
           NOT A DIGITAL LIST PRICE COMMERCIAL PRODUCT WHICH HAS BEEN SUBJECTED
           TO DIGITAL'S FULL COMMERCIAL QUALITY CONTROL AND PRODUCT VALIDATION
           PROCESSES. THE LICENSED SOFTWARE THUS MAY CONTAIN DEFECTS WHICH
           DIGITAL HAS NO OBLIGATION TO REMEDY.

     7.2.  To the best of DIGITAL's knowledge without conducting product
           clearance analyses or searches in the public records of the patent,
           copyright, and trademark offices throughout the world, DIGITAL has
           the right to use and to license the use of the LICENSED SOFTWARE in
           accordance with the terms and conditions of this Agreement.

     7.3.  The names used to identify each tool are for reference only. These
           names have been used internal to DIGITAL Only. These names are not
           to be confused with any external commercial product by the same name
           and may not be available for public use. SIMPLEX shall adopt its own
           unique and distinct names for each such CAD tool which it licenses
           to its customers and shall be solely responsible for clearance of
           the use of such names as trademarks/service marks for any SIMPLEX
           SOFTWARE and for defending and selling or otherwise satisfying any
           claim for infringement of any trademark or service rights anywhere
           in the world regarding the use by SIMPLEX of any such name.

     7.4.  THE WARRANTIES SET FORTH IN THIS ARTICLE 7 ARE IN LIEU OF ALL OTHER
           WARRANTIES, EXPRESS OR IMPLIED, AND DIGITAL EXPRESSLY DISCLAIMS ANY
           IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR
           PURPOSE.



*Certain information on this page has been omitted and filed separately with
 the Commission. Confidential treatment has been requested with respect to the
 omitted portions.

                                                                               5
<PAGE>   8
8.      ARTICLE 8 - LIMITATION OF LIABILITY

        8.1.    IN NO EVENT SHALL EITHER PARTY BE LIABLE FOR SPECIAL,
                INCIDENTAL, OR CONSEQUENTIAL DAMAGES, INCLUDING LOST PROFITS OR
                LOSS OF USE, OR OTHER ECONOMIC LOSS OF ANY SORT. EXCEPT AS
                PROVIDED UNDER SECTION 9.3 BELOW, DIGITAL SHALL NOT BE LIABLE TO
                SIMPLEX, AND DISCLAIMS ALL LIABILITY TO ANY OTHER PERSON OR
                ENTITY IN CONNECTION WITH THIS AGREEMENT, FOR THE USE OR
                PERFORMANCE OF THE LICENSED SOFTWARE, INCLUDING WITHOUT
                LIMITATION ANY LIABILITY FOR NEGLIGENCE IN TORT. SIMPLEX SHALL
                NOT BE LIABLE TO DIGITAL, AND DISCLAIMS ALL LIABILITY TO ANY
                OTHER PERSON OR ENTITY IN CONNECTION WITH THIS AGREEMENT, FOR
                THE USE OR PERFORMANCE OF THE SIMPLEX SOFTWARE INCLUDING,
                WITHOUT LIMITATION, ANY LIABILITY FOR NEGLIGENCE IN TORT.

9.      ARTICLE 9 - REMEDIES

        9.1.    In the event a third party asserts a claim of intellectual
                property infringement, DIGITAL has no obligations to obtain
                rights to continue the use of any such LICENSED SOFTWARE which
                is the subject of such claim.

        9.2.    DIGITAL agrees, at its own expense, to defend or at its option
                to settle, any claim or action brought against SIMPLEX on the
                issue of infringement of any copyright or trade secret right of
                any third party by the LICENSED SOFTWARE as used or distributed
                within the scope of the licenses granted under this Agreement
                and to indemnify SIMPLEX against all damages and costs,
                including legal fees, which may be incurred by SIMPLEX under any
                such claim or action; provided that SIMPLEX provides DIGITAL
                with (i) prompt written notice of such claim (ii) sole control
                and authority over the defense or settlement thereof, and (iii)
                proper and full information and assistance (at DIGITAL's
                expense, except for the cost of SIMPLEX's employee's time) to
                settle and/or defend any such claim or action.

        9.3.    Notwithstanding the provisions of Section 9.2 above, DIGITAL
                assumes no liability for infringement claims which would not
                exist but for (i) the combination of any LICENSED SOFTWARE with
                other software not provided by DIGITAL, or (iii) the
                modification of the LICENSED SOFTWARE unless such modification
                was made by DIGITAL.

        9.4.    SIMPLEX agrees, at its own expense, to defend or at its option
                to settle, any claim or action brought against DIGITAL on the
                issue of infringement of any copyright or trade secret right of
                any third party by the SIMPLEX SOFTWARE as used or distributed
                within the scope of the licenses granted under this Agreement
                and to indemnify DIGITAL against all damages and costs,
                including legal fees, which may be incurred by DIGITAL under any
                such claim or action; provided that DIGITAL provides SIMPLEX
                with (i) prompt written notice of such claim (ii) sole control
                and authority over the defense or settlement thereof, and (iii)
                proper and full information and assistance (at SIMPLEX's
                expense, except for the cost of DIGITAL's employee's time) to
                settle and/or defend any such claim or action.

                9.4.1.  Notwithstanding the provisions of Section 9.4 above,
                        SIMPLEX assumes no liability for infringement claims
                        which would not exist but for (i) the combination of
                        any SIMPLEX SOFTWARE with other software not provided
                        by SIMPLEX, or (iii) the modification of the SIMPLEX
                        SOFTWARE unless such modification was made by SIMPLEX.

        9.5     THE REMEDIES SET FORTH IN THIS ARTICLE 9 CONSTITUTES EACH
                PARTY'S EXCLUSIVE REMEDIES FOR INTELLECTUAL PROPERTY
                INFRINGEMENT, AND DEFECTS (WHETHER PATENT OR LATENT) IN THE
                LICENSED SOFTWARE OR SIMPLEX SOFTWARE AS APPLICABLE.

10.     ARTICLE 10 - INJUNCTIVE RELIEF

        10.1.   The parties hereby declare that the respective rights of the
                parties under Sections 2 or Section 4 are of a unique nature,
                the loss of which may cause

                                                                               6

<PAGE>   9
            irreparable harm, and that it may be impossible to measure in money
            the damages which will accrue to a party hereto by reason of the
            loss of such rights. Accordingly, in the event of any breach or
            threatened breach of Sections 2 or Section 4, the party whose
            software or CONFIDENTIAL INFORMATION are the subject of such breach
            or threatened breach shall be entitled to a final order from a court
            of competent jurisdiction of injunctive and other equitable relief,
            and if any party hereto shall institute any action or proceeding to
            enforce by specific performance or other equitable relief the
            provisions hereof, any the party against whom such action or
            proceeding in brought hereby waives the claim or defense therein
            that such party has an adequate remedy at law, and such part shall
            not urge in any such action or proceeding the claim or defense that
            such remedy at law exists. This Section 10 shall not limit or
            constrain the right of a party to pursue and recover damages at law
            for breaches of this Agreement, including breaches of Section 2 or
            Section 4.

11.  ARTICLE 11 - TERMINATION

     11.1.   If either party hereto shall fail to perform or observe any of the
             terms and conditions to be performed or observed by it under this
             Agreement, the other party shall give written notice to the
             defaulting party specifying the respects in which the defaulting
             party has failed to perform or observe the terms and conditions of
             this Agreement, and in the event that any default so indicated is
             not remedied by the defaulting party within thirty (30) days after
             receipt of such notice, the party not in default may in its sole
             discretion thereafter elect to terminate this Agreement, and,
             except as otherwise provided herein to survive termination, this
             Agreement and all the future obligations owed and future rights
             granted herein to the defaulting party shall immediately terminate.

             11.1.1.  As used in this Agreement the term "breach" or "default"
                      by a party shall mean a failure to perform or observe a
                      material term or provision hereof which remains uncurled
                      after the notice and time period set forth above. The
                      following events may constitute the breach of material
                      term of this Agreement.

                      11.1.1.1. a knowing and material violation of the
                                restrictions on license rights set forth herein.

                      11.1.1.2. failure by a party to follow proper procedures
                                for safeguarding CONFIDENTIAL INFORMATION under
                                this Agreement;

                      11.1.1.3. failure by SIMPLEX to make payment when due;

                      11.1.1.4. breach of warranty of either SIMPLEX or DIGITAL
                                and

                      11.1.1.5. failure of DIGITAL to provide training and
                                support services pursuant to Article 5 above.

      11.2.  On or before thirty (30) days prior to the expiration of the TERM
             of this Agreement, the parties may meet in person or by phone to
             determine whether and under what conditions this Agreement may be
             renewed.

      11.3.  The parties hereto agree that the termination of this Agreement
             shall not release either party from any other liability which shall
             have accrued to the other party at the time such termination
             becomes effective (provided that a remedy for such liability has
             not been expressly provided in this Agreement), nor affect in any
             manner the survival of any right, duty or obligation of either
             party which is expressly stated elsewhere in this Agreement to
             survive termination.

      11.4.  In the event of any termination of this Agreement for any reason,
             SIMPLEX shall no longer be entitled to continue to receive error
             corrections, updates and upgrades pursuant to section 5.1. However
             its rights to the LICENSED SOFTWARE existing as of the termination
             date shall continue.

12.  ARTICLE 12 - NOTICES

      12.1.  Any notice required or permitted to be given under this Agreement
             shall be sufficient as of three (3) days following the date of
             mailing if given by prepaid, first class, registered or certified
             mail addressed to the respective address, subject to change upon
             written notice, of the other Party as follows:

                                                                               7
<PAGE>   10
                    If DIGITAL:
                            John McClean
                            Acquisition Consultant
                            Digital Equipment Corporation
                            77 Reed Road
                            Hudson, MA 01749-2895
                    Copy to:
                            Digital Semiconductor General Counsel
                            Digital Equipment Corporation
                            111 Powdermill Road, MSO2-3
                            Maynard, MA 01754
                    If to LICENSEE:
                            Resve Saleh
                            President
                            Simplex Solutions, Inc.
                            2540 North First Street, Suite 302
                            San Jose, CA 95131
13.  ARTICLE 13 - GENERAL TERMS
     13.1. Waiver/Amendment: No waiver, amendment, or modification of any
           provision of this Agreement shall be effective unless in writing and
           signed by the party against whom such waiver, amendment or
           modification is sought to be enforced.
     13.2. Assignment or Transfer: Except as otherwise stated herein, SIMPLEX
           may not assign or transfer in any manner, including by operation of
           law, any of its rights or obligations under this Agreement to any
           third party integrated circuit manufacturer (including, but not
           limited to, Intel or National Semiconductor, etc.) without the
           express written consent of DIGITAL. Any assignment or transfer made
           without such consent shall be void.
     13.3. The recipient of DIGITAL technical information agrees not to
           export/re-export this technical information or any direct/immediate
           product of the technical information to any country proscribed under
           the U.S. Export Administrating Regulations, Parts 700 and 779.4
           (Country Groups Q, S, W, Y, and Z and the People's Republic of China
           and Afghanistan) without first receiving authorization from the U.S.
           Department of Commerce.
     13.4. Choice Of Law And Forum: The rights of the parties hereunder shall be
           governed by the laws of the State of California, U.S.A. Any
           litigation between the parties shall be commenced and prosecuted in
           California.
     13.5. Severability: If any provision of this Agreement shall be held by a
           court of competent jurisdiction to be contrary to law, the remaining
           provisions of this Agreement shall remain in full force and effect,
           and shall be interpreted to effect the intentions of the parties
           interpretations as if such provision has never been in this
           Agreement.
     13.6. Publicity:
           13.6.1. Each party shall use its reasonable and diligent efforts not
                   to disclose to any third party the terms and conditions of
                   this Agreement during its TERM, except as required by law, or
                   by governmental regulation, requirement or order, or as may
                   be necessary to establish or assert its rights hereunder, or
                   pursuant to confidentiality obligations, to bankers and other
                   financing sources and to auditors, attorneys and other
                   experts as deemed necessary by SIMPLEX to obtain financing.
           13.6.2. Notwithstanding the proscriptions of Article 13.6.1 above,
                   DIGITAL and SIMPLEX shall cooperate in preparing a press
                   release and a public announcement of the occurrence of this
                   Agreement, each of which shall occur within thirty (30) days
                   following the execution of this Agreement.
           13.6.3. DIGITAL shall have the right to review any subsequent press
                   releases or other promotional advertising or materials of
                   SIMPLEX that refer to DIGITAL, which shall be provided to
                   DIGITAL thirty (30) days in advance

                                                                               8
<PAGE>   11
             of release. If such releases, advertising or materials is found
             unacceptable by DIGITAL, SIMPLEX will revise the same in accordance
             with DIGITAL's wishes. DIGITAL shall review any such releases,
             plans or materials within 21 days and give written notice to
             SIMPLEX of approval or disapproval. DIGITAL's review team shall
             consist of at least one representative from the DIGITAL. SIMPLEX
             understands and agrees that the guidelines which DIGITAL shall use
             will be the absence from any such press release or other
             promotional material of any mention that any LICENSED SOFTWARE
             received from DIGITAL has been used, or is currently being used, by
             DIGITAL to design any specific semiconductor device, including by
             way of example only, DIGITAL's DECchip 21064 and subsequent chips
             utilizing the "ALPHA" architecture, and including any names used
             formally or informally by DIGITAL or in the industry or industry
             press, such as "ALPHA chips" or "ALPHA microprocessors" or the
             like. Once DIGITAL has found a particular press release, or piece
             of advertising or promotional material to be accepted, further
             publication approval by DIGITAL shall not be required for such
             release or piece of material.

     13.6.4. Notwithstanding the foregoing, SIMPLEX, without the approval of
             DIGITAL, shall have the right to indicate to the public that
             SIMPLEX has licensed the LICENSED SOFTWARE from DIGITAL, by using
             the notice "portions of this product incorporated technology
             licensed from DIGITAL EQUIPMENT CORPORATION", or the substantial
             equivalent thereof.

13.7. No prior condemnation, waiver, overlooking or lack of notice of any act
      or event giving rise to a right by either party to terminate shall operate
      to restrict, limit, or otherwise affect a subsequent right to either party
      to terminate this Agreement because of any act or event of a same or
      different nature.

13.8. Entire Agreement: This Agreement constitutes the complete and entire
      agreement between the parties with respect to the subject matter addressed
      herein, and merges all prior proposals and negotiations, whether oral or
      written, and all other prior communications and agreements between the
      parties with respect to such matter.

IN WITNESS WHEREOF, the parties hereto have as of the effective date first above
written caused this Agreement, including Appendix A which hereby is incorporated
by reference, to be signed in duplicate by their duly authorized
representatives.

DIGITAL EQUIPMENT CORPORATION         SIMPLEX SOLUTIONS, INC.

/s/ Robert Ed Caldwell                /s/ Resve Saleh
----------------------------          ----------------------------

Name: Robert Ed Caldwell              Name: Resve Saleh

Title: Vice President                 Title: President
       Digital Semiconductor

Date: 9/22/95                         Date: 9/25/95
<PAGE>   12
                APPENDIX A -- LICENSED SOFTWARE & DOCUMENTATION

The following are the CAD tools referenced in this agreement.

All these tools are purchased on the basis "as is". DIGITAL does not have any
obligation to add or change anything. It is a free will of DIGITAL
SEMICONDUCTOR / SEG / CAD group to release updates when and if they are
available. The Source Code will be supplied for all the software listed below.

[*]



*Certain information on this page has been omitted and filed separately with
 the Commission. Confidential treatment has been requested with respect to the
 omitted portions.
<PAGE>   13

6.   Library Utilities

[*]

The following are the supporting documentation for the above tools:

[*]



*Certain information on this page has been omitted and filed separately with
 the Commission. Confidential treatment has been requested with respect to the
 omitted portions.