A thin-film device comprises: a substrate; a flattening film made of an insulating material and disposed on the substrate; and a capacitor provided on the flattening film. The capacitor incorporates: a lower conductor layer disposed on the flattening film; a dielectric film disposed on the lower conductor layer; and an upper conductor layer disposed on the dielectric film. The thickness of the dielectric film falls within a range of 0.02 to 1 .mu.m inclusive and is smaller than the thickness of the lower conductor layer. The surface roughness in maximum height of the top surface of the flattening film is smaller than that of the top surface of the substrate and equal to or smaller than the thickness of the dielectric film. The surface roughness in maximum height of the top surface of the lower conductor layer is equal to or smaller than the thickness of the dielectric film.