The efficiency of light emitting diode (LED) is limited because large amount of generated light is confined inside of it by total internal reflection. A photonic crystal (PC) layer embedded in LED structure substantially modifies the guiding properties inside the chip and prevents the lateral propagation of light, so that it largely increases the output power of an LED. In this paper, we present both numerical and experiment studies on the enhancement of light extraction of GaN-based light-emitting diodes (LEDs) with hexagonal PC layer. By finite difference time domain (FDTD) simulation, the PC parameters were varied in order to evaluate the enhancement. Best extraction efficiency was obtained with the lattice constant of 400 - 600 nm, the PC thickness of 150 - 200 nm and the ratio of hole radius to lattice constant of 0.3 - 0.4 for the 465 nm LED based on GaN. Furthermore, hexagonal PC GaN-based LED was fabricated using anodic aluminum oxide (AAO) method. The PC layer is located below quantum well active layer and the efficiency was improved more than 20%. It was shown that these numerical results agree reasonably well with the experimental results.© (2007) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.