Provided is a semiconductor device including an oxide semiconductor and having stable electrical characteristics. Specifically, a semiconductor device including an oxide semiconductor and including a gate insulating film with favorable characteristics is provided. Further, a method for manufacturing the semiconductor device is provided. The semiconductor device includes a gate electrode, a gate insulating film over the gate electrode, an oxide semiconductor film over the gate insulating film, and a source electrode and a drain electrode in contact with the oxide semiconductor film. The gate insulating film includes at least a silicon oxynitride film and an oxygen release type oxide film which is formed over the silicon oxynitride film. The oxide semiconductor film is formed on and in contact with the oxygen release type oxide film.