An X-ray image sensor which includes: a photoelectric conversion part effecting electric charges in accordance with received amount of X-ray; a pixel electrode for collecting the electric charges; a storage capacitor for storing the electric charges collected in the pixel electrode, having a first capacitor electrode, a dielectric layer deposited on the first capacitor electrode and a second capacitor electrode on the dielectric layer, the second capacitor electrode contacting the pixel electrode through a first contact hole formed in a protection film on the second capacitor electrode; and a switching part controlling release of electric charges stored in the storage capacitor to an outer circuit. By the present invention, the switching characteristics of the TFT is enhanced by way of forming a two-layered protection film of silicon nitride and BCB on the channel portion of TFT, the capacity of the parasitic capacitor, which exists between the pixel electrode and the TFT, can be decreased.