There is provided a semiconductor device comprising:
a pixel portion comprising an n-channel thin film transistor or a CMOS circuit comprising an n-channel thin film transistor and a p-channel thin film transistor, the n-channel thin film transistor comprising:
a gate electrode, the gate electrode comprising:
a first layer made of a semiconductor film in contact with a gate insulating film;
and
a second layer in contact with the first layer;
a semiconductor layer, the semiconductor layer comprising:
a channel formation region;
a first impurity region of one conductivity type; and
a second impurity region of the one conductivity type between the channel formation region and the first impurity region ; and

wherein a part of the second impurity region overlaps with the first layer through the gate insulating film, and
wherein the second impurity region is in contact with the channel formation region.