Patent ID: 8546182

Claim:
A method of manufacturing a semiconductor device comprising the steps of: forming a first non-single crystalline oxide semiconductor film over a substrate by sputtering, the first non-single crystalline oxide semiconductor film including a region to become a channel region of a transistor; forming a second non-single crystalline oxide semiconductor film over the first non-single crystalline oxide semiconductor film by sputtering, the second non-single crystalline oxide semiconductor film having a lower conductivity than the first non-single crystalline oxide semiconductor film; etching the first non-single crystalline oxide semiconductor film and the second non-single crystalline oxide semiconductor film to form a first oxide semiconductor layer and a second oxide semiconductor layer on the first oxide semiconductor layer; forming an insulating film on the second oxide semiconductor layer, wherein each of the first non-single crystalline oxide semiconductor film and the second non-single crystalline oxide semiconductor film comprises indium and oxygen.