Off current of a thin film transistor is reduced, and on current of the thin film transistor is increased, and variation in electric characteristics is reduced. As a structure of semiconductor layers which form a channel formation region of a thin film transistor, a first semiconductor layer including a plurality of crystalline regions is provided on a gate insulating layer side; a second semiconductor layer having an amorphous structure is provided on a source region and drain region side; an insulating layer with a thickness small enough to allow carrier travel is provided between the first semiconductor layer and the second semiconductor layer. The first semiconductor layer is in contact with the gate insulating layer. The second semiconductor layer is provided on an opposite side to a face of the first semiconductor layer which is in contact with the gate insulating layer.