An organic light emitting diode (OLED) is capable of improving light efficiency per pixel unit by forming a cathode electrode to cover an anode electrode, thereby focusing light emitted from a luminescent layer per pixel unit. The OLED comprises: a second insulating film formed on a substrate including a TFT with source/drain electrodes formed on a first insulating film; a lower electrode formed on the second insulating film and connected to one of the source/drain electrodes; a third insulating film having an opening for exposing a portion of the lower electrode; a luminescent layer formed on the lower electrode inside the opening; a groove formed to surround the luminescent layer; and an upper electrode formed on the substrate including the groove so that the upper electrode surrounds the luminescent layer. The upper electrode functions as a reflection layer for reflecting total light while light emitted from the luminescent layer is being pulled out through the substrate.