An amorphous silicon thin film transistor, an organic light-emitting display (OLED) device including the same and method thereof are provided. The example amorphous silicon thin film transistor may include an amorphous silicon thin film transistor portion including a gate electrode, a gate insulating layer, an amorphous silicon layer, and source/drain electrodes and a heat generating portion generating heat and applying the heat to the amorphous silicon layer to reduce a threshold voltage of the amorphous silicon thin film transistor portion. The example method may include applying heat to an amorphous silicon layer if a threshold voltage of an amorphous silicon thin film transistor rises above a default level, the amorphous silicon thin film transistor including the amorphous silicon layer, the applied heat configured to reset the threshold voltage to the default level. The example OLED device may include a substrate and a plurality of pixels arranged in a matrix form on the substrate, each of the pixels comprising a switching transistor, a driving transistor, and an organic light-emitting diode.