An object of one embodiment of the present invention is to provide a highly reliable semiconductor device by giving stable electric characteristics to a transistor including an oxide semiconductor film. 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 provided over the oxide semiconductor film to overlap with the gate electrode layer, and a source electrode layer provided to cover an outer edge portion of the oxide semiconductor film. The outer edge portion of the drain electrode layer is positioned on the inner side than the outer edge portion of the gate electrode layer.