A semiconductor device (100A) includes a substrate (2), an oxide semiconductor layer (5) formed on the substrate (2), source and drain electrodes (6s, 6d) electrically connected to the oxide semiconductor layer (5), a first transparent electrode (7) electrically connected to the drain electrode (6d), a dielectric layer (8) formed on the source and drain electrodes (6s, 6d), and a second transparent electrode (9) formed on the dielectric layer (8). The upper and/or lower surface(s) of the first transparent electrode (7) contacts with a reducing insulating layer (8a) with the property of reducing an oxide semiconductor included in the oxide semiconductor layer (5). The second transparent electrode (9) overlaps at least partially with the first transparent electrode (7) via the dielectric layer (8). The oxide semiconductor layer (5) and the first transparent electrode (7) are formed out of the same oxide film.