ELECTROSTATIC BREAKDOWN PROTECTION CIRCUIT AND SEMICONDUCTOR INTEGRATED CIRCUIT

PROBLEM TO BE SOLVED: To protect a prescribed internal circuit disposed on an SOI substrate from electrostatic breakdown regardless of a positive or negative electrostatic surge.SOLUTION: An electrostatic breakdown protection circuit is provided on an SOI substrate 20 equipped with a first transistor TH operating on a first operating voltage and a second transistor TL operating on a second operating voltage lower than the first operating voltage and comprises at least the second transistor. The electrostatic breakdown protection circuit is configured so that resistance values of a source 1L and a drain 6L of the second transistor become smaller than resistance values of a source 1H and a drain 6H of the first transistor. Sources and drains of a plurality of second transistors are connected in series with each other at least between an input terminal and a ground terminal, between an output terminal and a ground terminal, or between a power terminal and a ground terminal.