Sen. Roland Burris of Illinois, who was appointed last year to replace President Obama in the Senate, has decided he won't run in next year's election, after his Senate service was clouded by controversy, FOX News has confirmed.

Burris plans a formal announcement Friday in Chicago.

Burris reportedly reached his decision after struggling to raise campaign funds -- an estimated $20,000 so far, with campaign disclosures with the Federal Election Commission expected to be filed next week.

A source told the Chicago Sun-Times that Burris has been very concerned about his legacy.

"After 20 years in government service, Burris didn't want the last four months in office to be that legacy," the source said.

Click here to read the Sun-Times report.

Gov. Rod Blagojevich appointed Burris on Dec. 30 to fill Obama's former seat over the objections of Senate Democratic leaders, who eventually welcomed Burris after being confronted with racial pressure. Burris is the Senate's only black member.

At the time, Blagojevich faced a federal probe into evidence he had attempted to sell the appointment, and the Illinois Legislature later ousted him from the governor's office.

Burris has denied paying for the appointment, though he has been alienated in the Senate since revelations he had not been forthright about communications with Blagojevich's camp.

By not seeking a full term, Burris increases Democrats chances of holding on to the Senate seat in 2010. Republicans had viewed Burris as a potentially easy target if he were to run for a full-term in the Senate.

Republican Rep. Mark Kirk of Illinois announced earlier this week his intent to run for the seat.