A semiconductor device includes a first semiconductor chip operating at a first power supply voltage and a second semiconductor chip operating at a second power supply voltage lower than the first power supply voltage to supply the second power supply voltage to the first semiconductor chip. The first semiconductor chip includes an output circuit including a first transistor and a second transistor, interconnected in series and turned on or off complementarily. The output circuit outputs a signal to a first external output terminal. The first semiconductor chip also includes a third transistor connected in series with the first and second transistors and having a gate electrode connected to a second output terminal.