The present invention provides a semiconductor device that is inexpensive and can suppress signal transmission delay, and a manufacturing method thereof. The semiconductor device includes: a plurality of semiconductor chips; a semiconductor substrate that has, on the same surface thereof, a chip-to-chip interconnection for electrically connecting the plurality of semiconductor chips to each other, and a plurality of chip-connection pads connected to the chip-to-chip interconnection; and a wiring board that has a plurality of lands of which pitch is larger than a pitch of the chip-connection pads, wherein a major surface of each of the plurality of semiconductor chips is connected to the chip-connection pads via a first connector so that the plurality of semiconductor chips are mounted on the semiconductor substrate, and an external-connection pad is formed on the major surface other than a region facing the semiconductor substrate, and is connected to the land on the wiring board via a second connector.