Philadelphia police say 20-year-old Lance Cpl. Nicholas Green was shot in the stomach around 1:40 a.m. Friday.
He's been taken to Temple University Hospital, where he's listed in critical condition.
Investigators say Green was apparently shot after he resisted when the gunman demanded money.
Police are still seeking the gunman.
Green is from the suburb of Media, Pa. He is a combat illustrator assigned to the Cherry Point, N.C, Marine Corps Air Station.
He is also a 2008 graduate of Strath Haven High School.