A semiconductor substrate includes a p-type substrate body, an n-type buried layer on the p-type substrate body, and a p-type semiconductor layer on the n-type buried layer. A DTI region penetrates through the p-type semiconductor layer and the n-type buried layer, and reaches the p-type substrate body. An n-type semiconductor region, which is a cathode region of a Zener diode, and a p-type anode region of the Zener diode are formed in the semiconductor layer. The p-type anode region includes a p-type first semiconductor region formed under the n-type semiconductor region, and a p-type second semiconductor region formed under the p-type first semiconductor region. A PN junction is formed between the p-type first semiconductor region and the n-type semiconductor region. An impurity concentration of the p-type second semiconductor region is higher than an impurity concentration of the p-type first semiconductor region.