Patent attributes
A semiconductor device in which a shift of the threshold voltage of a transistor is suppressed is provided. A semiconductor device in which a decrease in the on-state current of a transistor is suppressed is provided. The semiconductor device is manufactured as follows: forming a gate electrode layer over a substrate; forming a gate insulating film over the gate electrode layer; forming an oxide semiconductor film over the gate insulating film; forming a metal oxide film having a higher reducing property than the oxide semiconductor film over the oxide semiconductor film; performing heat treatment while the metal oxide film and the oxide semiconductor film are in contact with each other, thereby the metal oxide film is reduced so that a metal film is formed; and processing the metal film to form a source electrode layer and a drain electrode layer.
