A semiconductor device includes a layered region (104) formed in a semiconductor substrate (101) of a first conductivity type, and an electrode pad (106) formed on the semiconductor substrate with an interlayer insulating film (105) interposed therebetween and placed above the layered region. The layered region includes a first impurity diffusion region (102), a second impurity diffusion region (103) formed on the first impurity diffusion region, and a third impurity diffusion region (102x) formed on the first impurity diffusion region and surrounding a periphery of the second impurity diffusion region. a conductivity type of the first impurity diffusion region and a conductivity type of the third impurity diffusion region are a second conductivity type, and a conductivity type of the second impurity diffusion region is the first conductivity type. An impurity concentration of the third impurity diffusion region is higher than an impurity concentration of the first impurity diffusion region, and the third impurity diffusion region is electrically connected to a terminal fixed to a constant potential.