Abstract: An electrostatic protection circuit of a semiconductor device comprises a first MOS transistor of specific conductive type and a second MOS transistor of the specific conductive type. In the first MOS transistor, a drain thereof is connected to an output terminal or an input terminal and a source thereof is connected to a first power terminal and the first MOS transistor is controlled to be on/off by a signal received by a gate or ordinarily turned off by holding the gate at a specific potential. In the second MOS transistor of the specific conductive type, a drain thereof is connected to the output terminal or the input terminal and a source thereof is connected to a gate of the first MOS transistor and the second MOS transistor is ordinarily turned off by connecting a gate thereof to the first power terminal.