Jeremih -- Busted for DUI ... Happy Birthday!

R&B star Jeremih rang in his birthday by singing the DUI blues -- he got arrested early Friday morning in the Valley ... TMZ has learned.

The "Don't Tell 'Em" singer was pulled over by California Highway Patrol around 2:15 AM and booked for misdemeanor DUI.

Jeremih turned 28 on Friday ... so, we're guessing he was out celebrating. He ended up spending the rest of the night behind bars. Bail was set at $15k, and he was released around 11 AM.

Hope the turn up was good ... 'cause tonight's gonna suck.