A package structure of a compound semiconductor device comprises a thin film substrate, a die, at least one metal wire and a transparent encapsulation material. The thin film substrate comprises a first conductive film, a second conductive film, and an insulating dielectric material. The die is mounted on the surface of the first conductive film, and is electrically connected to the first conductive film and the second conductive film through the metal wire. The transparent encapsulation material overlays the first conductive film, second conductive film, and die. The surfaces of the first conductive film and second conductive film which is opposite the transparent encapsulation material act as electrodes. The insulating dielectric material is between the first conductive film and second conductive film.