A semiconductor device includes a substrate, a first semiconductor auxiliary film, a semiconductor film, a gate insulating film, and a gate electrode. The first semiconductor auxiliary film is provided in a selective region on the substrate. The semiconductor film includes an oxide semiconductor material, and has a low-resistive region in contact with the first semiconductor auxiliary film and a channel region provided in a portion different from the low-resistive region. The gate insulating film covers the semiconductor film from the channel region to at least part of the low-resistive region. The gate electrode is opposed to the channel region of the semiconductor film via the gate insulating film.