An active layer side silicon wafer is heat-treated in an oxidizing atmosphere to thereby form a buried oxide film therein. The active layer side silicon wafer is then bonded to a supporting side wafer with said buried oxide film interposed therebetween thus to fabricate an SOI wafer. Said oxidizing heat treatment is carried out under a condition satisfying the following formula: [Oi].ltoreq.2.123.times.10.sup.21exp(-1.035/k(T+273)), where, T is a temperature of the heat treatment, and [Oi] (atmos/cm.sup.3) is an interstitial oxygen concentration.