This semiconductor device (100A) includes: a gate electrode (3) formed on a substrate (2); a gate insulating layer (4) formed on the gate electrode; an oxide layer (50) which is formed on the gate insulating layer and which includes a semiconductor region (51) and a conductor region (55); source and drain electrodes (6s, 6d) electrically connected to the semiconductor region; a protective layer (11) formed on the source and drain electrodes; and a transparent electrode (9) formed on the protective layer. At least part of the transparent electrode overlaps with the conductor region with the protective layer interposed between them. The upper surface of the conductor region contacts with a reducing insulating layer (61) with the property of reducing an oxide semiconductor included in the oxide layer. The reducing insulating layer is out of contact with the channel region of the semiconductor region.