A thin film transistor including: a substrate; an active layer formed over the substrate; a gate insulating layer formed over the active layer; a gate electrode formed over the gate insulating layer; an interlayer insulating layer formed over the gate electrode; and source and drain electrodes that contact the active layer via the interlayer insulating layer. The source and drain electrodes may have a structure including an aluminum (Al) layer, an aluminum-nickel alloy (AlNiX) layer, and an indium tin oxide (ITO) layer, which are sequentially stacked.