A semiconductor device that can prevent reduction in the amplitude of electromagnetic waves transmitted from a reader/writer, and can prevent heating of an element forming layer due to a change in a magnetic field. The semiconductor device of the invention has an element forming layer formed over a substrate, and an antenna connected to the element forming layer. The element forming layer has at least wires such as a power supply wire and a ground wire that are arranged in a non-circular shape. The element forming layer and the antenna may be provided so as to overlap each other at least partially. The antenna may be provided above or below the element forming layer.