In an antenna and a semiconductor device including the antenna, an object is to reduce the distance between electrodes of a capacitor as much as possible, reduce the area of the electrode of the capacitor as much as possible, and prevent the suppression of response sensitivity and a response range of the semiconductor device. The present invention relates to an antenna including an antenna coil provided over a first region of a base and a capacitor which uses a second region of the base as a dielectric body and which has electrodes provided for opposite planes of the second region of the base, wherein the second region of the base is thinner than the first region of the base, and also relates to a semiconductor device including the antenna.