Hydrogen gas is ion-implanted into a silicon wafer for active layer via an insulating film, and thus ion-implanted wafer is then bonded with a supporting wafer via an insulating film interposed therebetween. This bonded wafer is heated to 500° C., so that a part of the bonded wafer is cleaved and separated, thereby producing an SOI wafer. Subsequently, thus-obtained SOI wafer is subjected to a heat treatment in an argon gas atmosphere. After that, the SOI wafer is subjected to an oxidation process in an oxidizing atmosphere, and thus formed oxide film is removed using an HF solution. Consequently, the surface of the SOI wafer is recrystallized and thus planarized.