A semiconductor device includes a thin-film transistor. The thin-film transistor comprises an oxide semiconductor layer, a gate insulating layer, a gate electrode overlapped on the oxide semiconductor layer through the gate insulating layer, a source electrode in contact with the oxide semiconductor layer, a drain electrode in contact with the oxide semiconductor layer and n (n is a natural number) metal layer(s) in contact with the oxide semiconductor layer and disposed across the oxide semiconductor layer between the source electrode and the drain electrode. The oxide semiconductor layer has (n+1) channel regions between the source electrode and the drain electrode in a plan view.