The present invention is intended to provide, in MOS transistors used as a bonding layer for silicon regions of an SOI substrate, an nMOS transistor on a silicon region of an SOI substrate which uses a polycrystalline silicon layer as a layer to be bonded with the silicon substrate and a pMOS transistor on another silicon region of the SOI substrate and electrically isolated back gate electrodes through a back gate insulation film on the silicon region side between the silicon regions and a polycrystalline silicon layer. A leak current is reduced and a malfunction of the transistors is eliminated by providing pickup electrodes for the back gate electrodes.