DeBarge Brother -- Sentenced to 6 Months in Jail After Drug Arrest

Mark DeBarge (from DeBarge) will spend half a year behind bars after his April drug arrest -- and he can look forward to some hefty community service too ... TMZ has learned.

We broke the story ... Mark was busted along with a female companion in a Hollywood hotel room ... after the woman's parole officer stopped by for a routine check and discovered narcotics.

Mark was charged with felony drug possession in addition to misdemeanor possession of drug paraphernalia. He was also charged with possession of a fake ID.

Mark pled "no contest" earlier this month to all three counts -- and was sentenced to 180 days behind bars. He was also sentenced to 30 days community service with Caltrans ... and 3 years formal probation.