Thin film transistor and display device

A semiconductor device comprising:

• a gate electrode over a substrate;
• a gate insulating layer over the gate electrode;
• a conductive layer over the gate insulating layer, the conductive layer having an opening and overlapping with the gate electrode;
• a buffer layer over the conductive layer, the buffer layer having an opening;
• an amorphous semiconductor layer over the buffer layer, the amorphous semiconductor layer having a region where the amorphous semiconductor layer is directly in contact with the gate insulating layer through the opening in the buffer layer and the opening in the conductive layer;
• a first impurity semiconductor layer over the amorphous semiconductor layer, the first impurity semiconductor layer overlapping with the region;
• a second impurity semiconductor layer over the amorphous semiconductor layer, the second impurity semiconductor layer overlapping with the conductive layer;
• a first wiring over the first impurity semiconductor layer, the first wiring being in contact with the first impurity semiconductor layer;
• and
• a second wiring over the second impurity semiconductor layer, the second wiring being in contact with the second impurity semiconductor layer.