A DC-DC converter is driven by single high input voltage, and includes a voltage converter circuit and a control circuit. The increase of the occupied area of the DC-DC converter is suppressed. The DC-DC converter includes an input terminal to which input voltage is applied; a voltage converter circuit connected to the input terminal, and including a first transistor; a control circuit configured to control the voltage converter circuit, and including a second transistor including a silicon material in a channel formation region; and a third transistor provided between the input terminal and the control circuit, and configured to convert the input voltage into power supply voltage that is lower than the input voltage. The first transistor and the third transistor include an oxide semiconductor material in channel formation regions. The first transistor and the third transistor are stacked over the second transistor with an insulating film provided therebetween.