A miniaturized transistor having high electrical characteristics is provided with high yield. In a semiconductor device including the transistor, high performance, high reliability, and high productivity can be achieved. The semiconductor device includes a base insulating film, an oxide semiconductor film with a bottom surface and side surfaces in the base insulating film and a top surface exposed from the base insulating film, a source electrode and a drain electrode over the base insulating film and the oxide semiconductor film, a gate insulating film over the oxide semiconductor film, the source electrode, and the drain electrode, and a gate electrode over the gate insulating film and overlapping the oxide semiconductor film.