A semiconductor device is provided which includes an N-type semiconductor layer and a P-type semiconductor layer coexisting in the same wiring layer without influences on the properties of a semiconductor layer. The semiconductor device includes a first wiring layer with a first wiring, a second wiring layer with a second wiring, and first and second transistors provided in the first and second wiring layers. The first transistor includes a first gate electrode, a first gate insulating film, a first oxide semiconductor layer, a first hard mask layer, and first insulating sidewall films covering the sides of the first oxide semiconductor layer. The second transistor includes a second gate electrode, a second gate insulating film, a second oxide semiconductor layer, and a second hard mask layer.