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.