A radiation detector of this invention has a curable synthetic resin film covering exposed surfaces of a radiation sensitive semiconductor layer, a carrier selective high resistance film and a common electrode, in which a material allowing no chloride to mix in is used in a manufacturing process of the curable synthetic resin film. This prevents pinholes and voids from being formed by chlorine ions in the carrier selective high resistance film and semiconductor layer. Also a protective film which does not transmit ionic materials may be provided between the exposed surface of the common electrode and the curable synthetic resin film, thereby to prevent the carrier selective high resistance film from being corroded by chlorine ions included in the curable synthetic resin film, and to prevent an increase of dark current flowing through the semiconductor layer.