Each pixel of the organic light-emitting display apparatus comprises a plurality of sub-pixels by using an organic light-emitting transistor (OLET). The OLET includes a plurality of gate electrodes that have different areas and are arranged adjacent to one another, a plurality of source electrodes and a plurality of drain electrodes, and an organic thin film layer disposed between or below the source electrodes and drain electrodes, the organic thin film layer including an organic light-emitting material, wherein the sub-pixels of the pixel selected by a scan signal are selectively turned-on/off by a data signal to represent a gradation.