Provided is a semiconductor device in which a plurality of chips are packaged without increasing the thickness of the package. A plurality of semiconductor elements (a first and a second semiconductor elements) that are packaged in the semiconductor device are overlaid with each other. Specifically, the first semiconductor element is fixed on the top surface of the first island while the second semiconductor element is fixed on the bottom surface of the second island. Furthermore, each of the islands (a first and a second islands) on which the semiconductor elements are respectively mounted in the present invention provides a structure has an irregular shape, and the islands are overlaid with each other along the sides of the semiconductor element to be mounted.