PURPOSE: To reduce a level difference between a silicon layer and a gate insulating film and prevent the disconnection of a gate electrode by forming the gate insulating film by thermal oxidation after forming a second silicon layer on a first silicon layer formed on an insulating substrate.

CONSTITUTION: On a substrate 201, a first silicon layer 202 composed of a source/drain area and a channel area, a gate insulating film 203 formed by thermally oxidizing a second silicon layer accumulated on the first silicon layer 202 and a gate electrode 204 are provided. A source/drain electrode 207 is connected with the source area and the drain area of the silicon layer 202 through a contact hole 206 opened on a interlayer insulating film 205. Thus, a level difference that the gate electrode 204 must pass over is reduced and the disconnection of the gate electrode 204 is prevented without using the material and the formation used for the gate electrode 204.