To improve noise immunity of a semiconductor device. A wiring substrate of a semiconductor device includes a first wiring layer where a wire is formed to which signals are sent, and a second wiring layer that is mounted adjacent to the upper layer or the lower layer of the first wiring layer. The second wiring layer includes a conductor plane where an aperture section is formed at a position overlapped with a portion of the wire 23 in the thickness direction, and a conductor pattern that is mounted within the aperture section of the conductor plane. The conductor pattern includes a main pattern section (mesh pattern section) that is isolated from the conductor plane, and plural coupling sections that couple the main pattern section and the conductor plane.