One object of the present invention is to increase an aperture ratio of a semiconductor device. A pixel portion and a driver circuit are provided over one substrate. The first thin film transistor (TFT) in the pixel portion includes: a gate electrode layer over the substrate; a gate insulating layer over the gate electrode layer; an oxide semiconductor layer over the gate insulating layer; source and drain electrode layers over the oxide semiconductor layer; over the gate insulating layer, the oxide semiconductor layer, the source and drain electrode layers, a protective insulating layer which is in contact with part of the oxide semiconductor layer; and a pixel electrode layer over the protective insulating layer. The pixel portion has light-transmitting properties. Further, a material of source and drain electrode layers of a second TFT in the driver circuit is different from a material of those of the first TFT.