A thin-film transistor includes a substrate (10), a gate electrode (20) provided on a portion of the substrate, an insulation layer (30) arranged to cover the gate electrode and the substrate, a source or drain (40) provided on the insulation layer in a region corresponding to a region of the gate electrode, a semiconductor layer (50) arranged to cover the source or drain (40) and the insulation layer, a drain or source (60) provided on the semiconductor in a portion of a region corresponding to a region of the source or drain (40) that overlaps with the gate electrode, and a channel (70) formed between the source or drain (40) and the drain or source (60) and having a length defined by a film thickness of the semiconductor layer (50).