A TFT includes a substrate, a transparent semiconductor layer on the substrate, the transparent semiconductor layer including zinc oxide and exhibiting a surface roughness of about 1.3 nm or less, a gate electrode on the transparent semiconductor layer, a gate insulating layer between the gate electrode and the transparent semiconductor layer, the gate insulting layer insulating the gate electrode from the transparent semiconductor layer, and source and drain electrodes on the substrate, the source and drain electrodes being in contact with the transparent semiconductor layer.