Abstract: The AlGaInP red-light emitting diode(LED) devices were fabricated by metal organic chemical vapor deposition(MOCVD) on GaAs substrate and the top GaP-layer were covered with indium tin oxide(ITO) transparent conductive coatings.The influence of the ITO thickness on the characteristics of the LED devices; including the surface/interface microstructures,photoelectric behavior,thermal stability,bonding states of In/O and light emission angle,was investigated with scanning/transmission electron microscopy(SET/TEM),X-ray photoelectron spectroscopy(SPS) and conventional probes.The results show that the ITO coating thickness had a major impact.To be specific,as the ITO thickness increased,the forward voltage of LED devices deceased,the emission light brightness changed in an increase-decrease manner,and the thermal stability increasingly improved,accompanied by a decrease of LED light emission angle.Possible mechanism(s) was tentatively discussed.We suggest that an optimized thickness of ITO coating be 200 ~300 nm.