There is provided a method of fabricating a 
silicon-on-insulator substrate, including the steps of (a) forming a 
silicon substrate at a surface thereof with an 
oxygen-containing region containing 
oxygen at such a concentration that 
oxygen is not precipitated in the oxygen-containing region in later mentioned heat treatment, (b) forming a 
silicon oxide film at a surface of the silicon substrate, (c) implanting 
hydrogen ions into the silicon substrate through the 
silicon oxide film, (d) overlapping the silicon substrate and a support substrate each other so that the 
silicon oxide film makes contact with the support substrate, and (e) applying heat treatment to the thus overlapped silicon substrate and support substrate to thereby separate the silicon substrate into two pieces at a region into which the 
hydrogen ions have been implanted, one of the two pieces remaining on the 
silicon oxide film as a silicon-on-insulator 
active layer. The support substrate, the silicon 
oxide film located on the support substrate, and the silicon-on-insulator 
active layer formed on the silicon 
oxide film defines a silicon-on-insulator structure. The method makes it possible to significantly reduce 
crystal defect density in the silicon-on-insulator 
active layer, which ensures that a substrate made in accordance with the method can be used for fabricating electronic devices thereon.