An input circuit has at least an enhancement type first MISFET incorporated between an input terminal and a power supply terminal for the input circuit. A gate electrode of the first MISFET is connected to the power supply terminal, and at least a second MISFET is incorporated between the input terminal and a gate electrode of a third MISFET constituting the input circuit. A gate electrode of the second MISFET is connected to the power supply terminal, whereby the dielectric breakdown of the gate of the third MISFET is prevented.
In an integrated circuit having an amplifier with its input terminal connected to a signal input terminal, a D.C. voltage bias circuit is provided which includes a D.C. bias voltage generator and a depletion mode MOS transistor connected at its source-drain path between the bias voltage generator and the signal input terminal and coupled at its gate electrode to either its source or its drain thus preventing breakdown of the gate insulating film of the depletion mode MOS transistor resulting from a surge voltage from the signal terminal.
