PURPOSE: To obtain a thin film SOI whose thickness is controlled, with excellent reproducibility, by a method wherein impurity whose segregation coefficient in silicon is smaller than 1 is introduced into a polysilicon film or an amorphous silicon film formed in an island type, melting recrystallization is performed by using aperture parts as species crystal, and a high concentration layer only is etched.

CONSTITUTION: On a silicon oxide film 2, a polysilicon film 5 or an amorphous silicon film is formed in an island type so as to contain a plurality of apertures formed in a part of the silicon oxide film 2 on a single crystal semiconductor substrate 1. Impurity 6 whose segregation coefficient in silicon is smaller than 1 is introduced into the above film. By using the aperture parts 3 as species crystal, the polysilicon film 5 or the amorphous silicon film is melted and recrystallized. The recrystallized silicon film 5 is etched by technique wherein a silicon film containing impurity of high concentration is selectively etched. Thereby, crystal orientation is controlled, and an SOI thin film having uniform SOI film thickness in a wafer surface and between wafers can be formed.