Semiconductor device comprising oxide semiconductor layer

A semiconductor device comprising:

• a gate electrode layer on an insulating surface;
• a gate insulating layer over the gate electrode layer;
• an oxide semiconductor layer over the gate insulating layer, the oxide semiconductor layer comprising a channel formation region which overlaps with the gate electrode layer with the gate insulating layer therebetween;
• a first electrode over and in electrical contact with the oxide semiconductor layer, the first electrode comprising a metal layer or a metal alloy layer;
• an insulating layer over the first electrode and the oxide semiconductor layer, the insulating layer including an opening;
• and
• a transparent pixel electrode over the insulating layer,
• wherein the transparent pixel electrode is in direct contact with an upper surface of the oxide semiconductor layer in the opening of the insulating layer, and
• wherein the insulating layer is in contact with an upper surface of the oxide semiconductor layer at a region overlapping with the gate electrode layer.