An object is to prevent malfunction of a power device. In a semiconductor device for driving a power device for power supply, a buffer circuit and a level-shift circuit are configured by transistors having the same conductivity type. Furthermore, a capacitor is provided in the level-shift circuit, and a signal to be boosted is supplied to the capacitor and is boosted using capacitive coupling of the capacitor. Furthermore, a structure can be employed in which the signal is boosted in such a manner that, in the level-shift circuit, a capacitor is provided between a wiring for supplying a low power source potential and a wiring for supplying a potential to boost the signal so that a power transistor can be driven.