The light extraction efficiency of light emitting diode (LED) devices was improved by embedding nano-sized two-dimensional, air cavity photonic crystal (PC) structure on the indium tin oxide (ITO) layer of GaN-based LEDs. The embedded air cavity PC structure was fabricated using a reversal imprint lithography technique. The nano-cavity patterns had a width of 560 nm, a space of 240 nm and a height of 280 nm. According to current-voltage characterization, the electrical performance of the LED devices was not degraded by the fabrication process of air cavity PC structure. The optical output power of the LED device was increased by up to 10% at a drive current of 20 mA by forming the nano-cavity PC structure on the transparent electrode of the blue LED device, which was grown on a patterned sapphire substrate, to maximize the photon extraction. Since photons are scattered with cavities and are unaffected by the packaging process, which is the encapsulation of a LED device with epoxy resin, this enhancement in light extraction efficiency will not be decreased after the packaging process. (C) 2012 Elsevier B. V. All rights reserved.