A support-side substrate having a thermal oxide film on the major surface is bonded to an active-layer-side substrate having a thermal oxide film on the major surface while making the major surfaces oppose each other. The active-layer-side substrate and part of the oxide film are selectively etched from a surface opposite to the major surface of the active-layer-side substrate to a halfway depth of the buried oxide film formed from the thermal oxide films at the bonding portion. A sidewall insulating film is formed on the etching side surface portion of the active-layer-side substrate. Then, the remaining buried oxide film except that immediately under the active-layer-side substrate is selectively etched. A single-crystal semiconductor layer is formed on the support-side substrate exposed by removing the buried oxide film.