An oxide film is formed on an SOI layer, an isolation oxide film and a gate electrode. A nitride film is formed on the oxide film. Next, anisotropic etching is performed only on the nitride film to form sidewalls on opposite side surfaces of the gate electrode. Thus, the oxide film is not etched. Next, an N-type impurity is implanted through the oxide film to form source/drain regions in an upper portion of the SOI layer. In this step, adjusting the implantation energy so that the impurity reaches the buried oxide film provides the source/drain regions in contact with the buried oxide film.