A level shifter including a transistor that can be formed through the same process as a display portion is provided. A semiconductor device serves as a level shifter including transistors having the same conductivity type. The semiconductor device includes a so-called MIS capacitor in which metal, an insulator, and a semiconductor are stacked as a capacitor for boosting an input signal. Since the MIS capacitor is used, the gate-source voltage of a transistor for generating an output signal can be increased. Thus, boosting operation to generate the output signal can be performed more surely.