Ex-USC wide receiver Joseph Lewis has been released from jail after serving nearly 6 months of his sentence in his domestic violence case ... TMZ Sports has learned. 

As we previously reported, 19-year-old Lewis was arrested back in July after his GF told police he had punched, scratched and strangled her during an argument. 

Lewis pled no contest to 1 felony domestic violence charge -- and also admitted guilt in a previous domestic violence incident. 

He was sentenced to a year in county jail -- but got out after roughly 6 months due to overcrowding and good behavior.