Document:

<PAGE>
                                                                     Ex. 10.13

                First Amendment to Credit Terms and Conditions
                            and Attachment Thereto

This First Amendment ("Amendment") amends that certain Credit Terms and
Conditions, ("Credit Terms and Conditions") dated June 25, 1999, by and
between Imperial Bank ("Bank") and Silicon Laboratories, Inc. ("Borrower")
and the Commitment Letter attached thereto dated April 19, 1999 (the
"Commitment Letter"), (collectively herein the Credit Terms and Conditions
and the Commitment Letter are referred to as the "Agreement") as follows:

1.     The last paragraph of the Credit Terms and Conditions is hereby
       amended in full to read as follows:

       "The Commitment Letter dated, December 9, 1999 as may be amended or
replaced, (the "Letter") is attached hereto and incorporated herein by this
reference for additional terms. In the event of a conflict between this
Agreement and the term of the Letter shall take precedence."

2.     Except as provided above, the Agreement remains unchanged.

3.     This Amendment is effective as of December 16, 1999, and the parties
       hereby confirm that the Agreement as amended is in full force and effect.

SILICON LABORATORIES, INC.

By: /s/ Navdeep S. Sooch
   ----------------------------------------
Name: Navdeep S. Sooch
     --------------------------------------
Title: Chairman and Chief Executive Officer
      -------------------------------------

By: /s/ John McGovern
   ----------------------------------------
Name: John McGovern
     --------------------------------------
Title: Chief Financial Officer
      -------------------------------------

IMPERIAL BANK

By: /s/ Chris Jacomino
   ----------------------------------------
Name: Chris Jacomino
     --------------------------------------
      Commercial Loan Officer

                                       1<PAGE>

   [LOGO]
IMPERIAL BANK
 MEMBER FDIC
<TABLE>
<CAPTION>
                                PROMISSORY NOTE
<S>            <C>         <C>         <C>        <C>   <C>         <C>      <C>      <C>
----------------------------------------------------------------------------------------------
  PRINCIPAL    LOAN DATE    MATURITY    LOAN NO   CALL  COLLATERAL  ACCOUNT  OFFICER  INITIALS
$2,000,000.00  12-16-1999  09-16-2003  721000049                    622074     619       CJ
----------------------------------------------------------------------------------------------
References in the shaded area are for Lender's use only and do not limit the applicability of
this document to any particular loan or item.
----------------------------------------------------------------------------------------------
BORROWER: SILICON LABORATORIES INC., A DELAWARE  LENDER: IMPERIAL BANK
          CORPORATION                                    EMERGING GROWTH INDUSTRIES GROUP -
          4635 BOSTON LANE                               SOUTHWEST REGIONAL OFFICE
          AUSTIN, TX 78735                               226 AIRPORT PARKWAY
                                                         SAN JOSE, CA 95110-1024
==============================================================================================
  PRINCIPAL AMOUNT: $2,000,000.00     INITIAL RATE: 8.500%     DATE OF NOTE: DECEMBER 16, 1999
</TABLE>

PROMISE TO PAY. SILICON LABORATORIES INC., A DELAWARE CORPORATION
("BORROWER") PROMISES TO PAY TO IMPERIAL BANK ("LENDER"), OR ORDER, IN LAWFUL
MONEY OF THE UNITED STATES OF AMERICA, THE PRINCIPAL AMOUNT OF TWO MILLION &
00/100 DOLLARS ($2,000,000.00) OR SO MUCH AS MAY BE OUTSTANDING, TOGETHER
WITH INTEREST ON THE UNPAID OUTSTANDING PRINCIPAL BALANCE OF EACH ADVANCE.
INTEREST SHALL BE CALCULATED FROM THE DATE OF EACH ADVANCE UNTIL REPAYMENT OF
EACH ADVANCE.

PAYMENT. BORROWER WILL PAY THIS LOAN IN ACCORDANCE WITH THE FOLLOWING PAYMENT
SCHEDULE:

        ADVANCES UNDER THE NOTE SHALL BE AVAILABLE THROUGH SEPTEMBER 16,
        2000 ("NON-REVOLVING DRAW PERIOD"). DURING THE NON-REVOLVING DRAW
        PERIOD, INTEREST ONLY SHALL BE DUE MONTHLY BEGINNING JANUARY 16,
        2000. ON SEPTEMBER 16, 2000, THE OUTSTANDING PRINCIPAL BALANCE OF
        THE ADVANCES UNDER THE NOTE SHALL BE PAYABLE MONTHLY IN 36 EQUAL
        PAYMENTS OF PRINCIPAL PLUS ACCRUED INTEREST BEGINNING OCTOBER 16,
        2000. ALL PRINCIPAL AND ACCRUED BUT UNPAID INTEREST SHALL IN ANY
        EVENT BE DUE AND PAYABLE ON OR BEFORE SEPTEMBER 16, 2003.

The annual interest rate for this Note is computed on a 365/360 basis; that
is, by applying the ratio of the annual interest rate over a year of 360
days, multiplied by the outstanding principal balance, multiplied by the
actual number of days the principal balance is outstanding. Borrower will pay
Lender at Lender's address shown above or at such other place as Lender may
designate in writing. Unless otherwise agreed or required by applicable law,
payments will be applied first to any unpaid collection costs and any late
charges, then to any unpaid interest, and any remaining amount to principal.

VARIABLE INTEREST RATE. The interest rate on this Note is subject to change
from time to time based on changes in an index which is the Imperial Bank
Prime Rate (the "Index"). The Prime Rate is the rate announced by Lender as
its Prime Rate of interest from time to time. Lender will tell Borrower the
current Index rate upon Borrower's request. Borrower understands that Lender
may make loans based on other rates as well. The interest rate change will
not occur more often than each day. THE INDEX CURRENTLY IS 8.500%. THE
INTEREST RATE TO BE APPLIED TO THE UNPAID PRINCIPAL BALANCE OF THIS NOTE WILL
BE AT A RATE EQUAL TO THE INDEX, RESULTING IN AN INITIAL RATE OF 8.500%.
NOTICE: Under no circumstances will the interest rate on this Note be more
than the maximum rate allowed by applicable law.

PREPAYMENT; MINIMUM INTEREST CHARGE. Borrower agrees that all loan fees and
other prepaid finance charges are earned fully as of the date of the loan and
will not be subject to refund upon early payment (whether voluntary or as a
result of default), except as otherwise required by law. In any event, even
upon full prepayment of this Note, Borrower understands that Lender is
entitled to a MINIMUM INTEREST CHARGE OF $250.00. Other than Borrower's
obligation to pay any minimum interest charge, Borrower may pay without
penalty all or a portion of the amount owed earlier than it is due. Early
payments will not, unless agreed to by Lender in writing, relieve Borrower of
Borrower's obligation to continue to make payments of accrued unpaid
interest. Rather, they will reduce the principal balance due.

LATE CHARGE. If a payment is 10 DAYS OR MORE LATE, Borrower will be charged
5.000% OF THE UNPAID PORTION OF THE REGULARLY SCHEDULED PAYMENT.

DEFAULT. Borrower will be in default if any of the following happens: (a)
"Borrower fails to make any payment when due which is not cured by Borrower
within ten (10) days of receipt of notice thereof". (b) Borrower breaks any
promise Borrower has made to Lender, or Borrower fails to comply with or to
perform when due any other term, obligation, covenant, or condition contained
in this Note or any agreement related to this Note, or in any other agreement
or loan Borrower has with Lender. (c) Any representation or statement made or
furnished to Lender by Borrower or on Borrower's behalf is false or
misleading in any meterial respect either now or at the time made or
furnished. (d) Borrower becomes insolvent, a receiver is appointed for any
part of Borrower's property, Borrower makes an assignment for the benefit of
creditors, or any proceeding is commenced either by Borrower or against
Borrower under any bankruptcy or insolvency laws. (e) Any creditor tries to
take any of Borrower's property on or in which Lender has a lien or security
interest. This includes a garnishment of any of Borrower's accounts with
Lender. (g) A material adverse change occurs in Borrower's financial
condition, or Lender believes the prospect of payment or performance of the
indebtedness is impaired.

If any default, other than a default in payment, is curable and if Borrower
has not been given a notice of a breach of the same provision of this Note
within the preceding twelve (12) months, it may be cured (and no event of
default will have occurred) if Borrower, after receiving written notice from
Lender demanding cure of such default: (a) cures the default within ten (10)
days; or (b) if the cure requires more than ten (10) days, immediately
initiates steps which Lender deems in Lender's sole discretion to be
sufficient to cure the default and thereafter continues and completes all
reasonable and necessary steps sufficient to produce compliance as soon as
reasonably practical.

LENDER'S RIGHTS. Upon default, Lender may declare the entire unpaid principal
balance on this Note and all accrued unpaid interest immediately due, without
notice, and then Borrower will pay that amount. Upon Borrower's failure to
pay all amounts declared due pursuant to this section, including failure to
pay upon final maturity, Lender, at its option, may also, if permitted under
applicable law, do one or both of the following: (a) increase the variable
interest rate on this Note to 5.000 percentage points over the Index, and (b)
add any unpaid accrued interest to principal and such sum will bear interest
therefrom until paid at the rate provided in this Note (including any
increased rate). Lender may hire or pay someone else to help collect this
Note if Borrower does not pay. Borrower also will pay Lender that amount.
This includes, subject to any limits under applicable law, Lender's
attorneys' fees and Lender's legal expenses whether or not there is a
lawsuit, including attorneys' fees and legal expenses for bankruptcy
proceedings (including efforts to modify or vacate any automatic stay or
injunction), appeals, and any anticipated post-judgment collection services.
Borrower also will pay any court costs, in addition to all other sums
provided by law. THIS NOTE HAS BEEN DELIVERED TO LENDER AND ACCEPTED BY
LENDER IN THE STATE OF CALIFORNIA. IF THERE IS A LAWSUIT, BORROWER AGREES UPON
LENDER'S REQUEST TO SUBMIT TO THE JURISDICTION OF THE COURTS OF LOS ANGELES
COUNTY, THE STATE OF CALIFORNIA. LENDER AND BORROWER HEREBY WAIVE THE RIGHT
TO ANY JURY TRIAL IN ANY ACTION, PROCEEDING, OR COUNTERCLAIM BROUGHT BY
EITHER LENDER OR BORROWER AGAINST THE OTHER. (INITIAL HERE JMcG, NSS) THIS
NOTE SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE
STATE OF CALIFORNIA.

DISHONORED ITEM FEE. Borrower will pay a fee to Lender of $25.00 if Borrower
makes a payment on Borrower's loan and the check or preauthorized charge with
which Borrower pays is later dishonored.

RIGHT OF SETOFF. Borrower grants to Lender a contractual security interest
in, and hereby assigns, conveys, delivers, pledges, and transfers to Lender
all Borrower's right, title and interest in and to, Borrower's accounts with
Lender (whether checking, savings, or some other account), including without
limitation all accounts held jointly with someone else and all accounts
Borrower may open in the future, excluding however all IRA and Keogh
accounts, and all trust accounts for which the grant of a security interest
would be prohibited by law. Borrower authorizes Lender, to the extent
permitted by applicable law, to charge or setoff all sums owing on this Note
against any and all such accounts.

LINE OF CREDIT. This Note evidences a straight line of credit. Once the total
amount of principal has been advanced, Borrower is not entitled to further
loan advances. Advances under this Note may be requested orally by Borrower
or by an authorized person. All oral requests shall be confirmed in writing
on the day of the request. All communications, instructions, or directions
by telephone or otherwise to Lender are to be directed to Lender's office
shown above. The following party or parties are authorized to request
advances under the line of credit until Lender receives from Borrower at
Lender's address shown above written notice of revocation of their authority:
JOHN MCGOVERN, CFO/SECRETARY; AND NAVDEEP S. SOOCH, CHAIRMAN/CEO. Borrower
agrees to be liable for all sums either: (a) advanced in accordance with the
instructions of an authorized person or (b) credited to any of Borrower's
accounts with Lender. The unpaid principal balance owing on this Note at any
time may be evidenced by endorsements on this Note or by Lender's internal
records, including daily computer print-outs. Lender will have no obligation
to advance funds under this Note if: (a) Borrower is in default under the
terms of this Note or any agreement that Borrower has with Lender, including
any agreement made in connection with the signing of this Note; (b) Borrower
ceases doing business or is insolvent; (c) (d) Borrower has applied funds
provided pursuant to this Note for purposes other than those authorized by
Lender; or (e)
<PAGE>

12-16-1999                      PROMISSORY NOTE                           Page 2
                                  (CONTINUED)
================================================================================
                                                    JMcG     NSS     CJ
                                                    -----   -----   ----

REFERENCE PROVISION.  1. Other than (i) non-judicial foreclosure and all
matters in connection therewith regarding security interests in real or
personal property; or (ii) the appointment of a receiver, or the exercise of
other provisional remedies (any and all of which may be initiated pursuant to
applicable law), each controversy, dispute or claim between the parties
arising out of or relating to this document ("Agreement"), which controversy,
dispute or claim is not settled in writing within thirty (30) days after the
"Claim Date" (defined as the date on which a party subject to the Agreement
gives written notice to all other parties that a controversy, dispute or
claim exists), will be settled by a reference proceeding in California in
accordance with the provisions of Section 638 et seq. of the California Code
of Civil Procedure, or their successor section ("CCP"), which shall
constitute the exclusive remedy for the settlement of any controversy,
dispute or claim concerning this Agreement, including whether such
controversy, dispute or claim is subject to the reference proceeding and
except as set forth above, the parties waive their rights to initiate any
legal proceedings against each other in any court or jurisdiction other than
the Superior Court in the County where the Real Property, if any, is located
or Los Angeles County if none (the "Court"). The referee shall be a retired
Judge of the Court selected by mutual agreement of the parties, and if they
cannot so agree within forty-five (45) days after the Claim Date, the referee
shall be promptly selected by the Presiding Judge of the Court (or his
representative). The referee shall be appointed to sit as a temporary judge,
with all of the powers for a temporary judge, as authorized by law, and upon
selection should take and subscribe to the oath of office as provided for in
Rule 244 of the California Rules of Court (or any subsequently enacted
Rule). Each party shall have one peremptory challenge pursuant to CCP 170.6
The referee shall (a) be requested to set the matter for hearing within sixty
(60) days after the Claim Date and (b) try any and all issues of law or fact
and report a statement of decision upon them, if possible, within ninety (90)
days of the Claim Date. Any decision rendered by the referee will be final,
binding and conclusive and judgment shall be entered pursuant to CCP 644 in
any court in the State of California having jurisdiction. Any party may apply
for a reference proceeding at any time after thirty (30) days following
notice to any other party of the nature of the controversy, dispute or claim,
by filing a petition for a hearing and/or trial. All discovery permitted by
this Agreement shall be completed no later than fifteen (15) days before the
first hearing date established by the referee. The referee may extend such
period in the event of a party's refusal to provide requested discovery for
any reason whatsoever, including, without limitation, legal objections raised
to such discovery or unavailability of a witness due to absence or illness.
No party shall be entitled to "priority" in conducting discovery. Depositions
may be taken by either party upon seven (7) days written notice, and request
for production or inspection of documents shall be responded to within ten
(10) days after service. All disputes relating to discovery which cannot be
resolved by the parties shall be submitted to the referee whose decision
shall be final and binding upon the parties. Pending appointment of the
referee as provided herein, the Superior Court is empowered to issue
temporary and/or provisional remedies, as appropriate.

2. Except as expressly set forth in this Agreement, the referee shall
determine the manner in which the reference proceeding is conducted including
the time and place of all hearings, the order of presentation of evidence,
and all other questions that arise with respect to the course of the
reference proceeding. All proceedings and hearings conducted before the
referee, except for trial, shall be conducted without a court reporter,
except that when any party so requests, a court reporter will be used at any
hearing conducted before the referee. The party making such a request shall
have the obligation to arrange for and pay for the court reporter. The costs
of the court reporter at the trial shall be borne equally by the parties.

3. The referee shall be required to determine all issues in accordance with
existing case law and the statutory laws of the State of California. The rules
of evidence applicable to proceedings at law in the State of California will
be applicable to the reference proceeding. The referee shall be empowered to
enter equitable as well as legal relief, to provide all temporary and/or
provisional remedies and to enter equitable orders that will be binding upon
the parties. The referee shall issue a single judgment at the close of the
reference proceeding which shall dispose of all of the claims of the parties
that are the subject of the reference. The parties hereto expressly reserve
the right to contest or appeal from the final judgment or any appealable
order or appealable judgment entered by the referee. The parties hereto
expressly reserve the right to findings of fact, conclusions of law, a
written statement of decision, and the right to move for a new trial or a
different judgment, which new trial, if granted, is also to be a reference
proceeding under this provision.

4. In the event that the enabling legislation which provides for appointment
of a referee is repealed (and no successor statute is enacted), any dispute
between the parties that would otherwise be determined by the reference
procedure herein described will be resolved and determined by arbitration.
The arbitration will be conducted by a retired judge of the Court, in
accordance with the California Arbitration Act, 1280 through 1294.2 of the
CCP as amended from time to time. The limitations with respect to discovery
as set forth hereinabove shall apply to any such arbitration proceeding.

CREDIT TERMS AND CONDITIONS AGREEMENT. This Note is subject to the provisions
of the Credit Terms and Conditions Agreement dated March 28, 1997 and all
amendments thereto and replacements therefor.

GENERAL PROVISIONS. Lender may delay or forgo enforcing any of its rights or
remedies under this Note without losing them. Borrower and any other person
who signs, or endorses this Note, to the extent allowed by law, waive any
applicable statute of limitations, presentment, demand for payment, protest
and notice of dishonor. Upon any change in the terms of this Note, and unless
otherwise expressly stated in writing, no party who signs this Note, whether
as maker, accommodation maker or endorser, shall be released from liability.
All such parties agree that Lender may renew or extend (repeatedly and for
any length of time) this loan, or release any party or guarantor or
collateral; or impair, fail to realize upon or perfect Lender's security
interest in the collateral; and take any other action deemed necessary by
Lender without the consent of or notice to anyone. All such parties also
agree that Lender may modify this loan without the consent of or notice to
anyone other than the party with whom the modification is made.

PRIOR TO SIGNING THIS NOTE, BORROWER READ AND UNDERSTOOD ALL THE PROVISIONS
OF THIS NOTE, INCLUDING THE VARIABLE INTEREST RATE PROVISIONS. BORROWER
AGREES TO THE TERMS OF THE NOTE AND ACKNOWLEDGES RECEIPT OF A COMPLETED COPY
OF THE NOTE.

BORROWER:

SILICON LABORATORIES INC., A DELAWARE CORPORATION

BY: /s/ John W. McGovern                 BY: /s/ Navdeep S. Sooch
   -------------------------------          -------------------------------
   JOHN MCGOVERN, CFO/SECRETARY             NAVDEEP S. SOOCH, CHAIRMAN/CEO

================================================================================

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