A configuration is adopted comprising an NchMOS transistor 1 equipped with an insulating isolation layer 4 providing insulation and isolation using an SOI structure, and a capacitor formed using an insulating film, with a silicon substrate B being made thin and substrate capacitance being reduced. The NchMOS transistor 1 is equipped with insulating isolation regions 5a, 5b that are perfectly depleted or partially depleted in a manner close to being perfectly depleted. An electrode 6 connected to a gate electrode G of the NchMOS transistor 1 and an impurity diffusion layer 7 are connected via a capacitor 2. A source electrode S is connected to a power supply terminal 3a, a gate electrode G is connected to an internal signal line S1, and a drain electrode D is connected to an internal signal line S2. Substrate bias voltage is then controlled using capacitor coupling when the NchMOS transistor 1 is turned on/off.