To provide a method for manufacturing a semiconductor device by which a well contact of a transistor is easy to obtain.

This method for manufacturing the semiconductor device includes a step for forming a silicon layer 30 having a first region and a second region on an insulating layer 20, a step for doping the first region of the silicon layer 30 with impurities, a step for forming a thermally-oxidized film 16 on the surface of the silicon layer 30 after doping with the impurities, a step for removing the thermally-oxidized film 16, a step for forming a first field oxide film 41 so as to contact to the insulating layer 20 in the first region, a step for forming a second field oxide film 42 over the insulating layer 20 with the silicon layer 30 between in the second region, a step for forming a fully-depleted type transistor on the silicon layer 30 in the first region, and a step for forming a partially-depleted type transistor on the silicon layer 30 in the second region.

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