A TFT includes a substrate, a source electrode and a drain electrode on the substrate, the source and drain electrodes separated from each other, an active layer on the substrate between the source electrode and the drain electrode, a cladding unit on side surfaces of the source electrode and the drain electrode, a gate insulating layer on the substrate, the gate insulating layer overlapping the active layer and the cladding unit, and a gate electrode on the gate insulating layer, the gate electrode overlapping the active layer.