PURPOSE:To contrive improvement in the degree of integration of the titled semiconductor device by a method wherein one transistor is replaced with a semiconductor element formed on an insulating film, and also an insulating film for element isolation is utilized as an insulating film thereof. CONSTITUTION:A selective etching is performed on a polycrystalline Si film 46 using an optical etching method, and polycrystalline Si films 47 and 48 are left on thermal oxide films 44 and 45 respectively. Then, a photoresist is applied on the whole surface, a part of the thermal oxide film 45 located on an Si thin film 43 is exposed by performing exposure and developing processes on said resist, and boron is implanted therein. Another photoresist 51 is applied on the whole surface again, the thermal oxide films 44 and 45 are partially exposed by performing exposure and developing processes on the resist 51, and phosphorus is ion-implanted. Then, an N<+> region 52, a source region 53 and a drain region 54 are exposed by performing a wet etching, and then the resist 51 is removed. Lastly, a source electrode 55, a drain electrode 56 and an anode electrode 57 are formed respectively.