The tunnel field-effect transistor includes a drain layer, a source layer, a channel layer, a metal gate layer, and a high-k dielectric layer. The drain and source layers are of opposite conductive types. The channel layer is disposed between the drain layer and the source layer. At least one of the drain layer, the channel layer, and the source layer has a substantially constant doping concentration. The metal gate layer is disposed around the channel layer. The high-k dielectric layer is disposed between the metal gate layer and the channel layer.