| abstract |
Stable electrical characteristics of the transistor including the oxide semiconductor layer are achieved. A highly reliable semiconductor device comprising such a transistor is provided. Such a semiconductor device includes a multilayer film composed of an oxide layer and an oxide semiconductor layer, a gate insulating film in contact with the oxide layer, and a gate electrode overlapping the multilayer film with a gate insulating film interposed therebetween. The oxide layer includes an element common to the oxide semiconductor layer, and has an energy gap larger than that of the oxide semiconductor layer. The composition between the oxide layer and the oxide semiconductor layer gradually changes. |