Kate Major Gets 6 Months in Jail

Kate Major's gonna pay BIG for her arrest last month -- a judge is locking her up for the next 6 months ... TMZ has learned.

Michael Lohan's estranged wife was sentenced Monday for violating probation. Her October arrest in Florida for attacking a cop triggered the violation ... according to the U.S. Attorney's Office.

Kate was already on probation for a 2015 incident in New Orleans when she allegedly got wasted on a plane and threatened the crew. Sources close to Kate tell us she asked for rehab instead of jail time but got shut down.