An object is to reduce the resistance of each member included in a transistor, to improve ON current of the transistor, and to improve performance of an integrated circuit. A semiconductor device including an n-channel FET and a p-channel FET which are provided over a single crystal semiconductor substrate with an insulating layer provided therebetween and are isolated by an element isolation insulating layer. In the semiconductor device, each FET includes a channel formation region including a semiconductor material, a conductive region which is in contact with the channel formation region and includes the semiconductor material, a metal region in contact with the conductive region, a gate insulating layer in contact with the channel formation region, a gate electrode in contact with the gate insulating layer, and a source or drain electrode partly including the metal region.