In an organic light-emitting display device and a method of manufacturing the same, the organic light-emitting display device comprises: a substrate including a transistor region; a buffer layer and a semiconductor layer sequentially formed on the substrate; a gate electrode formed on the semiconductor layer; an interlayer insulating film formed on the gate electrode; source and drain electrodes, each formed on the interlayer insulating film and having a portion penetrating the interlayer insulating film so as to contact the semiconductor layer; a mask pattern formed on each of the source and drain electrodes; and a pixel defined layer formed on the mask pattern.