Abstract: A first well of a first conductivity type is formed in a partial region of the surface layer of a semiconductor substrate. A MOS transistor is formed in the first well. The MOS transistor has a gate insulating film, a gate electrode, and first and second impurity diffusion regions of a second conductivity type on both sides of the gate electrode. A high leak current structure is formed which makes a leak current density when a reverse bias voltage is applied across the first impurity diffusion region and first well become higher than a leak current density when the same reverse bias voltage is applied across the second impurity diffusion region and first well.