PURPOSE: To make it possible to completely dielectric-isolate an element from other element by a method wherein an insulating film is formed in rectangular shape on a semiconductor crystal substrate, an epitaxially grown layer is formed on the insulating film, and after an insulating film has been formed on the insulating film removed part and the side face of the lattice-like groove formed by etching, the groove is filled up and its surface is flattened.

CONSTITUTION: Using a P-type silicon single crystal having a plane (100), a thermal oxide film is formed as an insulating film 2, and an epitaxially grown layer is grown along the plane (100) as far as to the oxide film by conducting dry etching of vapor phase epitaxy. Then, the above-mentioned layer is flattened by apply a resist and conducting dry etching thereon. The above-mentioned flattened surface is oxidized, and the thermally oxide film is etched in lattice form. An insulating film 4 is formed in the front by conducting silicon etching using the oxide film as a mask. Polysilicon is formed by a depression CVD method, and a groove part is filled up completely. A resist is applied, the oxide film on the surface is dry-etched, and an insular silicon single crystal which is completely dielectric-isolated can be obtained.