Burris was appointed by disgraced former Illinois Gov. Rod Blagojevich, who was impeached and driven from office after he was accused of trying to sell the seat.
The committee placed special emphasis on a phone conversation between Burris and the governor's brother, where Burris linked his willingness to raise funds for the governor with his desire for appointment to the Senate.
While finding no violation of law, the committee's "Public Letter of Qualified Admonition" told Burris that "senators must meet a much higher standard of conduct" than he exhibited with his constantly changing statements.
The ethics committee has often been criticized for failing to go beyond letters of admonition after finding a senator's conduct discredited the institution.
The letter had tough wording, telling Burris that he provided "inconsistent, misleading or incomplete information" to the public, the Senate and investigators; and that his conduct "reflected unfavorably on the Senate."
Senate Democratic leaders, however, expressed no desire to hand out further punishment.
Jim Manley, spokesman for Majority Leader Harry Reid, said, "The ethics committee handled its independent investigation, and its letter of qualified admonition speaks for itself."
Joe Shoemaker, spokesman for second-ranking Senate Democrat Dick Durbin, said the senior Illinois senator would not go beyond his statement that the ethics panel admonishment speaks for itself.
Durbin's statement said that Senate Democratic leaders made clear to Burris that in order to be seated, "he needed to appear before the Illinois General Assembly to testify openly, honestly and completely about the nature of his relationship with the former governor, his associates and the circumstances surrounding this appointment.
"Since then, the accuracy and completeness of his testimony and affidavits have been called into question. The U.S. Senate Ethics Committee has completed its review into this matter and found that Sen. Burris' actions have brought discredit on him and the Senate."
Burris commented, "I am pleased that after numerous investigations, this matter has finally come to a close. I thank the members of the Senate Ethics Committee for their fair and thorough review of this matter, and now look forward to continuing the important work ahead on behalf of the people of Illinois."
Weakened and facing multiple primary challengers next spring, Burris has decided not to fight for a full Senate term next year. Fellow Democrats shun him. Meanwhile, the former governor is scheduled to go to trial in June.
The ethics committee was especially critical of Burris' comments during the Nov. 13, 2008, phone call from the governor's brother.