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                                                                 EXHIBIT 10.6.1

                                 PROMISSORY NOTE


$1,500,000                                                    December 5, 2000


                FOR VALUE RECEIVED, the undersigned, CLAYTON A. THOMAS, JR. (the
"BORROWER") promises to pay to the order of NET2000 COMMUNICATIONS GROUP, INC.,
a Delaware corporation (the "LENDER"), the principal sum of ONE MILLION FIVE
HUNDRED THOUSAND DOLLARS ($1,500,000), or, if less, the aggregate outstanding
amount of the Loan defined in the Agreement referred to below, together with
interest thereon as set forth below, at its offices or such other place as the
Lender may designate in writing.

        1.      Agreement. This Promissory Note (the "NOTE") is executed and
delivered by the Borrower in connection with loans which may be made by the
Lender to the Borrower pursuant to the terms and conditions of that certain
letter agreement dated of even date herewith (as the same may be amended,
modified or restated from time to time, the "AGREEMENT") between the Borrower
and the Lender. This Note is subject to the terms and conditions of the
Agreement and is entitled to the benefits of the security described in and
provided for in the Pledge Agreement (as defined in the Agreement). Any
capitalized term used herein and not otherwise defined herein shall have the
meaning assigned to it in the Agreement.

        2.      Interest Rate Provisions. Except as provided in Section 2.2
hereof, from the date hereof and thereafter until the outstanding amount hereof
is paid in full, interest shall accrue on the principal balance of this Note
outstanding from time to time at the Prime Rate (as defined below) plus a margin
of 1% per annum (the "INTEREST RATE"), and shall be paid currently in cash on a
monthly basis on each Payment Date (as defined below).

                2.2     Default Interest Rate. If the Borrower shall default in
the payment of the principal of or interest on the Note or any other amount
becoming due hereunder after any applicable cure period, by acceleration or
otherwise, or under any other Document, whether or not such default is declared,
the Interest Rate shall increase to the Prime Rate plus a margin of 3% per annum
and interest shall be paid currently in cash on a monthly basis on each Payment
Date (as defined below) until the payment in full of all overdue payments or
other cure of such Event of Default.

                2.3     Calculation of Interest. Interest shall be computed for
each payment period on the principal balance for the actual number of days
outstanding over a year of 365 or 366 days, as applicable.

                As used herein, "Prime Rate" means, at any time, the greater of
the rate of interest per annum then most recently announced or established by
The Toronto Dominion Bank at its principal office in New York City as its
highest commercial prime or base rate then in effect. Each change in any
interest rate provided for herein based upon the Prime Rate resulting from a
change in the Prime Rate shall take effect without notice to the Borrower at the
time of such change in the Prime Rate.

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        3.      Payment Provisions.

                3.1     Interest Payments.

                        (a)     Pay Rate Interest. Commencing on the last day of
 the calendar month following the date the initial advance of the Loan is made
and continuing on the last day of each succeeding calendar month thereafter
(each such date, a "PAYMENT DATE"), the Borrower shall pay in cash to the Lender
monthly installments of interest only (in arrears) at the applicable Interest
Rate on the then outstanding principal balance under this Note.

                3.2     Principal Payments and Payment at Maturity. On the
Maturity Date, the entire then outstanding principal balance of this Note,
together with all accrued but unpaid interest, and all other sums owed hereunder
shall be due and payable in full in cash without further notice or demand.

                3.3     Prepayments; Application of Payments. The Borrower may
prepay the then outstanding principal amount of this Note in whole or in part at
any time without premium or penalty.

                3.4.    Mandatory Prepayment of the Note. In the event that the
Borrower is no longer employed by the Lender for any reason whatsoever (whether
because of termination, death or otherwise) (the first date on which Borrower is
no longer employed, the "TERMINATION DATE") the Loan, together with all accrued
interest therein and all other obligations payable pursuant to this Agreement,
the Note and the Pledge Agreement, shall become due and payable no later than
thirty (30) days from the Termination Date.

                3.5     Payments Generally. All payments of principal and
interest in respect of this Note shall be made in lawful money of the United
States of America in same day funds to the Lender, at its office located at 2180
Fox Mill Road, Herndon, Virginia 20171 or at such other place as shall be
designated in writing to the Borrower for such purpose.

        4.      Assignment. This Note and the obligations hereunder may not be
assigned by the Borrower without the prior written consent of the Lender.

        5.      Default and Remedies. The occurrence of an Event of Default
under the Agreement shall constitute a default hereunder and, so long as such
Event of Default shall continue, shall entitle the Lender to exercise the rights
and remedies specified in the Agreement, as well as those available at law or in
equity.

        6.      Waivers. The Borrower hereby waive presentment, demand, protest,
or further notice of any kind.

        7.      Controlling Law. This Note and all matters related hereto shall
be governed, construed and interpreted strictly in accordance with the laws of
the State of New York.
                           [Signatures on next page]


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               IN WITNESS WHEREOF, the undersigned has caused this Note to be
executed and its seal affixed on the day and year first above written.




                                     /s/Clayton A. Thomas, Jr.
                                     -------------------------------------------
                                     CLAYTON A. THOMAS, JR.




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COMMONWEALTH OF VIRGINIA)
                        )       ss:
COUNTY OF FAIRFAX       )


               On this 8th day of December, 2000, before me personally appeared
CLAYTON A. THOMAS, JR., to me known to be the person who executed the foregoing
instrument and who being by me duly sworn, did depose and say that he resides at
811 Water Place, Alexandria, Virginia and that he signed his name to the
foregoing instrument.

               SEAL
                                     /s/Jennifer S. Fabris
                                     -------------------------------------------
                                     NOTARY PUBLIC


My commission expires on:  5/31/2004