An organic light emitting display device may include a display panel, a source driving circuit, and a voltage generator. The display panel may include a pixel circuit including a driving transistor to drive an organic light emitting diode. The driving transistor may have four independent terminals including first and second gate electrodes. The source driving circuit may provide a data voltage to the pixel circuit. The voltage generator may apply an independent bias voltage to the second gate electrode of the driving transistor to control a driving voltage range of the driving transistor.