A convex polycrystalline silicon film is formed on a handle wafer. A semiconductor
layer is formed on the polycrystalline silicon film. The semiconductor is thinner
on its areas in which the convex polycrystalline silicon film is formed and is
thicker on its areas in which the convex polycrystalline silicon film is not formed.
An opening is formed in each of those areas of an insulating film which are located
under respective thick-film semiconductor areas of the semiconductor layer. The
polycrystalline silicon film is formed in the openings to connect electrically
the thick-film semiconductor areas and the handle wafer together.