A thin film transistor (TFT) and a method of fabricating the same are disclosed. The TFT includes a substrate, a gate electrode disposed over the substrate, a gate insulating layer disposed over the gate electrode, a semiconductor layer disposed over the gate insulating layer and including a polycrystalline silicon (poly-Si) layer, an ohmic contact layer disposed over a predetermined region of the semiconductor layer, an insulating interlayer disposed over substantially an entire surface of the substrate including the ohmic contact layer, and source and drain electrodes electrically connected to the ohmic contact layer through contact holes formed in the interlayer insulating layer. A barrier layer is interposed between the semiconductor layer and the ohmic contact layer. Thus, when an off-current of a bottom-gate-type TFT is controlled, degradation of characteristics due to a leakage current may be prevented using a simple process.