PURPOSE: To reduce the space for the incorporation in a semiconductor device which is integrated while including an output transistor (TR) without distorting the operation of the output TR by providing the circuit in which a TR and a Zener diode are combined at the output terminal of the output TR.

CONSTITUTION: When the output terminal voltage of the output TR1 exceeds the sum voltage of the operating voltage of the Zener diode 7 and the operating voltage of the TR formed of the emitter and base of a PNPTR6 owing to a positive external surge, the PNPTR6 turns on and the Zener diode 7 and collector of the TR6 absorb a current due to the surge to protect the output TR1, but the majority of the current passes through the collector and the current of the Zener diode 7 is only the base current of the TR6 and extremely small, thereby reducing the size. In this case, the operating voltage of the Zener diode 7 is about twice as high as the voltage of the power source Vcc and an increase in capacity viewed from the output TR1 is suppressed by the TR6, so the operation distortion of the output TR1 is suppressed.