An oxide thin film transistor (TFT) includes an oxide semiconductor layer including a first semiconductor layer and a second semiconductor layer on the first semiconductor layer; a gate insulating layer on the oxide semiconductor layer; a gate electrode on the gate insulating layer; an interlayer insulating layer on the gate electrode; and a source electrode and a drain electrode on the interlayer insulating layer and contacting the oxide semiconductor layer, wherein a first reflectance of the first semiconductor layer is greater than a second semiconductor layer.