A high-voltage oxide transistor includes a substrate; a channel layer disposed on the substrate; a gate electrode disposed on the substrate to correspond to the channel layer; a source contacting a first side of the channel layer; and a drain contacting a second side of the channel layer, wherein the channel layer includes a plurality of oxide layers, and none of the plurality of oxide layers include silicon. The gate electrode may be disposed on or under the channel layer. Otherwise, the gate electrodes may be disposed respectively on and under the channel layer.