Provided are a capacitor and a semiconductor device including the same. The capacitor includes a first electrode, a dielectric layer over the first electrode, a second electrode between the first electrode and the dielectric layer, and a third electrode over the dielectric layer and in contact with the dielectric layer such that the dielectric layer is between the second electrode and the third electrode. A thermal expansion coefficient of the first electrode may be greater than a thermal expansion coefficient of the dielectric layer, and a work function of the second electrode may be higher than a work function of the first electrode.