Jason "Mayhem" Millerhas officially been hit with felony domestic violence and resisting arrest charges, TMZ Sports has learned ... stemming from an incident where he allegedly roughed up his GF, and barricaded himself in a bathroom.
We broke the story ... Miller was arrested early in the morning last Friday, when cops received a call from a woman who was screaming for help. They rushed to the scene -- a home in L.A.'s San Fernando Valley -- and ultimately arrested Mayhem after cops say they found the woman with visible marks on her face and neck.
The L.A. County District Attorney filed criminal charges this week -- corporal injury to a spouse -- saying the MMA fighter "willfully inflicted corporal injury resulting in a traumatic condition" on his girlfriend.
Because he has multiple prior convictions for violent crimes, if convicted, Miller could face a lengthier prison sentence.
And now we're learning more about what allegedly happened during the incident.
Our law enforcement sources tell us Mayhem locked himself in a bathroom and refused to come out ... so cops were forced to knock down the door, in order to contact him.
We're also told the alleged female victim hopped out of a window to escape Miller.
For the two felony charges, Miller is facing years in prison.
The former UFC fighter is also currently being investigated for an alleged bar fight where he's been accused of breaking another man's ribs ... an incident that allegedly went down only days before his arrest for domestic violence.
Miller has not been arrested or charged with a crime stemming from that alleged incident.