In recent years, flat display panels such as liquid crystal panels and plasma display panels have been increasingly used as display elements for image display devices such as television receivers instead of conventional cathode-ray tubes, allowing for image display devices to be made thinner. In display panels used in such image display devices, a plurality of TFTs are provided in rows and columns as switching elements for controlling the operation of respective pixels. Conventionally, silicon semiconductors made of materials such as amorphous silicon and polycrystalline silicon were generally used for semiconductor films included in the TFTs. In recent years, however, it has been proposed that organic semiconductor films made of organic materials be used for the semiconductor films. Since organic semiconductor films can be formed at low temperatures, it is possible to form the films via a low cost coating process such as spin coating, and it is also possible to use a flexible substrate such as a plastic substrate, for example, in the device; thus, such a film is suitable for a flexible image display device. Patent Documents 1 and 2 disclose examples of semiconductor devices that use such an organic semiconductor film.