The invention eliminates a need to increase a size of a semiconductor device and reduces occurrence of noise. A semiconductor device of the invention includes: a base (5) having front layers (9, 11) provided on respective sides of a core layer (7) formed by a printed circuit board, and a semiconductor chip (1) mounted on the base (5), wherein the semiconductor chip (1) is joined to one (9) of the front layers by using a joining member (3), and the other front layer (11) has a plurality of external terminals (55) arranged thereon, and the core layer (7) has a plurality of through-holes (41, 43, 45, 75, 77) formed therein to electrically connect the semiconductor chip (1) to the plurality of external terminals (55) together, and the plurality of through-holes (41, 43, 45, 75, 77) include a plurality of arrayed through-holes (41, 43, 45) arranged correspondingly to the arrangement of the plurality of external terminals (55) and one or more additional through-holes (75, 77) formed between the plurality of arrayed through-holes (41, 43, 45).