A semiconductor device having an SOI structure having a contact for making steady the potential of a semiconductor substrate without involvement of an increase in the surface of the semiconductor device. In a semiconductor chip, an integrated circuit is fabricated within an internal circuit region, and a plurality of buffer circuits are fabricated within buffer regions. Wiring layers for supplying steady potential are formed in the area of the semiconductor chip other than the internal circuit region and the buffer regions; for example, at four corners of the semiconductor chip, and contacts for connecting the wiring layers and the semiconductor substrate are formed in the area of the integrated circuit which is not assigned for fabrication of integrated circuits, thus eliminating a necessity for ensuring a location specifically allocated for formation of the contacts.