Fallen hedge fund billionaire Raj Rajaratnam, convicted of Wall Street's biggest insider trading scam, is set to face his punishment in a Manhattan courtroom Thursday.

Rajaratnam, 54, who founded the Galleon Group, is to be sentenced five months after he was found guilty of 14 counts of conspiracy and security frauds that he committed while he ran the company.

The FBI, after its most extensive phone-tapping in a white-collar probe, arrested Rajaratnam on Oct. 16, 2009, on charges of insider trading, which forced the $7-billion valued Galleon Group to close down. He could face almost 25 years in prison.

His lawyer asked for a shorter term sentence arguing that Rajaratnam's health was poor and that he does not deserve a two-decade term.

Rajaratnam, a Sri Lankan-born U.S. citizen, is the principal figure in an insider trading network that touched some of America's top companies which include the Goldman Sachs Group Inc, Intel Corp, IBM and the elite McKinsey & Co. consultancy.

Rajaratnam made some $63.8 million in illegal profits.

U.S. District Judge Richard Holwell, who presided over the two-month trial, will deliver the sentence on Thursday.

Since his conviction, Rajaratnam has been under house arrest, on a bail of $100 million.

The Galleon case has rung an alarm bell throughout Wall Street and the hedge fund industry.

Out of 26 people who were charged in the Galleon case, Rajaratnam and three others were found guilty at trial and 21 other pleaded guilty, while one defendant is still at large.

According to legal experts, Rajaratnam is likely to get a sentence of eight to 20 years.

He might also be allowed to remain in home detention in his Manhattan apartment while he challenges the phone taps.

Rajaratnam was on the Forbes’ list of the richest Americans (No. 262) with net worth estimated at $1.8 billion, before he was arrested.