Abstract: A transistor includes a multilayer film in which an oxide semiconductor film and an oxide film are stacked, a gate electrode, and a gate insulating film. The multilayer film overlaps with the gate electrode with the gate insulating film interposed therebetween. The multilayer film has a shape having a first angle between a bottom surface of the oxide semiconductor film and a side surface of the oxide semiconductor film and a second angle between a bottom surface of the oxide film and a side surface of the oxide film. The first angle is acute and smaller than the second angle. Further, a semiconductor device including such a transistor is manufactured.

Abstract: It is an object to provide a semiconductor device including an oxide semiconductor, which has stable electric characteristics and high reliability. A semiconductor device having a stacked-layer structure of a gate insulating layer; a first gate electrode in contact with one surface of the gate insulating layer; an oxide semiconductor layer in contact with the other surface of the gate insulating layer and overlapping with the first gate electrode; and a source electrode, a drain electrode, and an oxide insulating layer which are in contact with the oxide semiconductor layer is provided, in which the nitrogen concentration of the oxide semiconductor layer is 2×1019 atoms/cm3 or lower and the source electrode and the drain electrode include one or more of tungsten, platinum, and molybdenum.