We have fabricated GaN-based light-emitting diodes (LEDs) using transparent indium tin oxide-based (ITO-based) p contacts. The current-voltage characteristics and life tests of GaN-based LEDs have been studied. LED life tests showed that a pure ITO contact layer had poor reliability at high current stress. We also found that the GaN-based LED could achieve good reliability with a NiO/ITO contact layer. Using transmission electron microscopy and energy-dispersive X-ray spectrometer analyses, we observed In-contained metallic interface between the p-GaN layer and the pure ITO contact layer after annealing at 600°C. It revealed that ITO would react at interface or indiffuse near the interface at 600°C. The LED was degraded with unstable interfaces after life tests (stressed by a 50-mA current injection). To improve the reliability of GaN-based LEDs with the ITO contact layer, we suggest that the NiO layer be used to prevent the reaction and block the leakage pathway.