A semiconductor device has a semiconductor chip, an internal circuit region arranged on an inner side of the semiconductor chip, and a bonding pad region arranged adjacently to the internal circuit region. A diode-type ESD protection circuit is formed of a junction between a first conductivity type diffusion layer for fixing a substrate potential of the semiconductor chip and a pair of second conductivity type diffusion layers arranged on an inner side of the first conductivity type diffusion layer. The first conductivity type diffusion layer is arranged on an entire peripheral region or a part of the peripheral region of the semiconductor chip with the peripheral region being outside of the internal circuit region and the bonding pad region. One of the pair of second conductivity type diffusion layers comprising a diffusion layer for breakdown adjustment at a junction portion with the first conductivity type diffusion layer.