To provide a highly reliable semiconductor device in which a transistor including an oxide semiconductor film has stable electric characteristics. The semiconductor device includes a gate electrode layer over a substrate, a gate insulating film over the gate electrode layer, an oxide semiconductor film over the gate insulating film, a drain electrode layer which is over the oxide semiconductor film so as to overlap with the gate electrode layer, and a source electrode layer provided so as to cover part of an outer edge portion of the oxide semiconductor film. An outer edge portion of the drain electrode layer is on an inner side than an outer edge portion of the gate electrode layer.