A technique capable of achieving both improvement of mounting density and noise reduction for a semiconductor device is provided. An LSI mounted on a printed wiring board comprises a grounding BGA ball and a power BGA ball to get power supply from the printed wiring board, and the grounding BGA ball and the power BGA ball are arranged closely to each other. A decoupling capacitor is mounted on the printed wiring board and has a first terminal and a second terminal. The grounding BGA ball and the first terminal are connected by a first metal electrode plate, and the power BGA ball and the second terminal are connected by a second metal electrode plate. The first metal electrode plate and the second metal electrode plate interpose a dielectric film having a thickness equal to or smaller than 1 μm therebetween.