1. A semiconductor substrate comprising a support member, an insulation layer arranged on the support member and a semiconductor layer arranged on the insulation layer, characterized in that: the outer peripheral extremity of said semiconductor layer is located inside the outer peripheral extremity of said support member and the outer peripheral extremity of said insulation layer is located between the outer peripheral extremity of said semiconductor layer and that of said support member so that the outer peripheral portion of the semiconductor substrate including said insulation layer and said semiconductor layer shows a stepped profile.