A thin Silicon film On Insulator (SOI) material fabricating method which is capable of providing a very high thickness uniformity of the silicon film, a process simplification and a considerable reduction of processing cost is disclosed, in which a silicon oxide film is formed on one or both of a p-type silicon bond wafer and a silicon base wafer, then the two wafers are bonded together through the silicon oxide film, subsequently a fixed positive charge is induced in the silicon oxide film to form a n-type inversion layer in the p-type silicon bond wafer adjacent to an interface between the p-type silicon bond wafer and the silicon oxide film layer, and thereafter a chemical etching is effected while applying a positive voltage to the p-type silicon bond wafer so that an etch-stop is made at an interface between a depletion layer including the n-type inversion layer and the p-type layer.