A method of manufacturing a display device includes forming a gate electrode on a substrate, a gate insulating layer on the gate electrode, and an active layer on the gate insulating layer, the gate electrode made of extrinsic polycrystalline silicon, the active layer made of intrinsic polycrystalline silicon; forming an etch stopper on the active layer; forming source and drain electrodes spaced apart from each other on the etch stopper; forming an ohmic contact layer each between a side of the active layer and the source electrode and between an opposing side of the active layer and the drain electrode; forming a gate line connected to the gate electrode; and forming a data line crossing the gate line.