Hydrogen gas is ion-implanted into a wafer for active layer via an oxide film. The wafer for active layer is bonded with a supporting wafer using the oxide film as the bonding surface. The bonded wafer is subjected to a heat treatment at the temperature in a range of 400.degree. C. to 1000.degree. C. As a result of this heat treatment, the bonded wafer is cleaved at the site of ion-implanted layer as the interface thereby producing an SOI wafer. In this heat treatment for cleavage, the temperature difference within the surface of the bonded wafer is controlled to be within 40.degree. C. Consequently, the wafer can be cleaved and separated completely across its entire surface at the site of the ion-implanted layer as the interface without leaving any regions uncleaved.