To downsize a semiconductor device comprising two MOSFET chips and capacitors, and to downsize a DC-DC converter and to improve its characteristic.

The semiconductor device comprises a first MOSFET chip with a drain terminal formed on one surface, and with a source terminal and a gate terminal formed on the other surface; a second MOSFET chip with a drain terminal formed on one surface, and with a source terminal and a gate terminal formed on the other surface; and a tabular capacitor with electrodes formed on both sides. The source terminal of the second MOSFET chip and the one electrode of the capacitor are laminated and electrically connected, and the drain terminal of the first MOSFET chip and the other electrode of the capacitor are laminated and electrically connected in the semiconductor device.