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 , 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 .