A change in electrical characteristics can be inhibited and reliability can be improved in a semiconductor device using a transistor including an oxide semiconductor. A semiconductor device includes a transistor which includes a gate electrode, a first insulating film over the gate electrode, an oxide semiconductor film over the first insulating film, a source electrode electrically connected to the oxide semiconductor film, and a drain electrode electrically connected to the oxide semiconductor film. A second insulating film is provided over the transistor, and a protective film is provided over the second insulating film. The second insulating film includes oxygen. The protective film includes at least one of metal elements used for the oxide semiconductor film.