Abstract: In an output buffer circuit, two P channel MOSFET's (1, 2) are connected in parallel between a power supply terminal (16) and an output terminal (10), and two N channel MOSFET's (3, 4) are connected in parallel between the ground terminal (17) and the output terminal (10). When a high potential is applied to the power supply terminal (16), either one of the P channel MOSFET's (1, 2) or either one of N channel MOSFET's (3, 4) is turned on in response to an input signal. When a normal power supply potential is applied to the power supply terminal (16), two P channel MOSFET's (1, 2) or two N channel MOSFET's (3, 4) are turned on in response to the input signal.

Abstract: An output circuit of a semiconductor circuit has a reverse bias voltage generator which comprises a ring oscillating circuit, a reverse bias voltage generating circuit and a switching circuit. The output circuit is of the type having first and second output N-(P-)channel MOS transistors connected in series, an output terminal being provided at the intermediate position of the transistors. The ring oscillating circuit is activated for oscillation only when an ouptut enabling signal is of a zero potential indicative of disabling outputting of an input data signal. The reverse bias voltage generating circuit generates a reverse bias voltage lower (higher) than the ground potential based on the oscillation output of the oscillating circuit. The switching circuit supplies a reverse bias voltage to the gate of the first output N-(P-)channel MOS transistor only when a bias instruction signal, i.e.