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                                                                  EXHIBIT 10.33
                              [AVANT! LETTERHEAD]


Viraj Patel
5080 Canyon Crest Drive
San Ramon, CA 94583

September 20, 2001

               This letter is being delivered to you by Avant! Corporation (the
"Company") to encourage you to continue your employment with the Company. The
Company hereby offers you a stay bonus, subject to the conditions set forth
below, equal to $280,000.00. The stay bonus will be paid in a lump sum by check,
subject to customary federal and state withholding requirements, on the three
month anniversary of the closing date of a Change of Control of the Company (the
"EFFECTIVE DATE") if the conditions set forth below for receipt of such stay
bonus have been met.

               In order to receive the stay bonus on the Effective Date, you
must not have resigned or have been terminated for Cause on or before the
Effective Date. If you resign, or are terminated for Cause on or prior to the
Effective Date, or are terminated without Cause before a definitive agreement
for a Change of Control of the Company is signed, you will not be entitled to
receive the stay bonus or any portion of the stay bonus (pro rata or otherwise).
If the Company terminates you without Cause after a definitive agreement for a
Change of Control of the Company has been signed and prior to the Effective
Date, you will still be entitled to receive your full stay bonus on the
Effective Date. You will not be entitled to any stay bonus or any portion of the
stay bonus (pro rata or otherwise), however, if before the Effective Date you
are offered another job with the Company or any of its affiliates, and you
accept such job offer.

               This letter, and the stay bonus it describes, is in addition to,
and not a substitute for, any other employment, compensation or severance
arrangements you may have with the Company. This Letter is not a guarantee of
employment and either you or the Company may terminate your at-will employment
at any time. You acknowledge that you have not received any assurances of
continued employment or employment for any specific duration.

You acknowledge that the terms and provisions of this letter were made and
entered into in strict confidence and must remain confidential. You further
agree that except as required by law, or in response to a subpoena or other
valid legal process, or in


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connection with an action to enforce the terms of this letter, you will not
disclose, privately or publicly, any of the terms or provisions of this letter
to anyone other than your spouse, or your attorneys, accountants or tax
advisors, and you agree to cause them to maintain such information in
confidence. In addition, you agree to keep confidential and not disclose,
privately or publicly, any information relating to any potential Change of
Control of the Company.

               Our agreement in this letter shall be governed by and construed
in accordance with the laws of the State of California.

               As used in this letter, the following terms shall have the
meaning set forth below:

        "CAUSE" means any material failure to perform your duties, any material
        breach of your duties, any dishonest or fraudulent actions or negligent
        or willful conduct or malfeasance, any criminal conduct, any breach of
        your duty of loyalty, any dishonesty or dishonest conduct in connection
        with your duties and your obligations to the Company, or any conduct
        that would have a material adverse effect on the Company or any of its
        operations.

        CHANGE OF CONTROL" means the occurrence of one or more of the following
        transactions by no later than June 30, 2002: (i) a merger or
        consolidation of the Company with or into another entity or any other
        corporate reorganization, if more than 50% of the combined voting power
        of the continuing or surviving entity's securities outstanding
        immediately after such merger, consolidation or other reorganization is
        owned by persons who were not stockholders of the Company immediately
        prior to such merger, consolidation or other reorganization, or (ii) the
        sale, transfer, exchange or other disposition of all or substantially
        all of the Company's assets.

               Please acknowledge your acceptance of and agreement to this
letter by signing below.

                                                   Very truly yours,
                                                   /S/ Clayton Parker
                                                   ------------------------
                                                   Clayton Parker
                                                   General Counsel

Accepted and Agreed:

/s/ Viraj J. Patel
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Viraj Patel
Head of Finance