A semiconductor device having high ESD resistance includes an internal circuit, an I/O pad, a division circuit connected to a lead-in line connecting the internal circuit and the I/O pad for outputting an electric signal from first and second terminals corresponding to an electric signal applied to the lead-in line and a clamp circuit including an MOS transistor for cutting off conduction when a difference in voltage between electric signals sent between the terminals is smaller in absolute value than a threshold voltage of the MOS transistor, and conducts when the absolute value is at least equal to the threshold voltage.