PURPOSE: To make it possible to form a single crystal thin film (SOI film) having excellent crystallizability by a method wherein a polishing work is performed using a selective polishing method having the polishing speed on an epitaxial crystal film higher than that of a polishing adjusting film.

CONSTITUTION: Insulating films 102 and 102' and silicon dioxide films 103 and 103', which are thicker than the insulating films, are formed on a P-type silicon crystal substrate 101, a seed hole 116 to be used for epitaxial growth of film is provided, and a silicon epitaxial crystal film 104 is selectively grown in the seed hole 116 only. Then, a polysilicon film 105 is formed thereon using a chemical vapor-deposition method, and the surface of said silicon substrate 101 is polished using a selective polishing method wherein the silicon polishing speed is sufficiently made higher than that of the silicon dioxide film. This polishing operation can be finished in the height of the silicon dioxide films 103 and 103' in an excellent controllable manner. As a result, an SOI film having excellent crystallizability can be formed easily by controlling film thickness in a highly precise manner, and the semiconductor device having the SOI film of excellent characteristics can be obtained as a part of its constituent element.