A semiconductor device is provided with a first well region of a first conduction type having a first voltage (voltage VB) applied thereto, a second well region of a second conduction type formed in the surface layer section of the first well region and having a second voltage (voltage VS) different from the first voltage applied thereto, and a charge extracting region of the first conduction type formed in the surface layer section of the second well region and having the first voltage applied thereto. This inhibits the operation of a parasitic bipolar transistor.