A semiconductor device includes a semiconductor substrate of a first conductivity type, an impurity layer of a second conductivity type provided within the semiconductor substrate, an impurity region of the second conductivity type that is connected, within the semiconductor substrate, to the impurity layer, and separates a first region of the semiconductor substrate from a second region by surrounding the first region of the semiconductor substrate together with the impurity layer, a first well and second well of the second conductivity type that are provided on the impurity layer via at least a semiconductor layer of the first conductivity type, and a plurality of transistors provided to the semiconductor substrate.