An organic light-emitting display device and a method of its manufacture are provided, whereby manufacturing processes are simplified and display quality may be enhanced. The display device includes: an active layer of a thin film transistor (TFT), on a substrate and including a semiconducting material; a lower electrode of a capacitor, on the substrate, doped with ion impurities, and including a semiconducting material; a first insulating layer on the substrate to cover the active layer and the lower electrode; a gate electrode of the TFT, on the first insulating layer; a pixel electrode on the first insulating layer; an upper electrode of the capacitor, on the first insulating layer; source and drain electrodes of the TFT, electrically connected to the active layer; an organic layer on the pixel electrode and including an organic emission layer; and a counter electrode facing the pixel electrode, the organic layer between the counter electrode and the pixel electrode.