An organic thin film transistor (OTFT) and an organic electroluminescent display (OLED) device are disclosed. The OTFT includes a drain electrode, functioning as a pixel electrode (anode electrode) of an organic emission element, such that the manufacturing process of an OLED device is simplified. In one embodiment, the OLED device includes: i) a substrate comprising an emission region and a non-emission region, ii) an organic thin film transistor, which comprises, a gate electrode, source and drain electrodes respectively overlapping both side portions of the gate electrode, and a semiconductor layer, and is disposed in the non-emission region, and iii) an organic light emitting element comprising a lower electrode, an organic layer, and an upper electrode. In one embodiment, one of the source electrode and drain electrode of the OTFT extends to the emission region, the semiconductor layer has an opening exposing a portion of the extending electrode, and the exposed portion of the extending electrode acts as a lower electrode (pixel or anode electrode) of the organic light emitting element.