An　optically　transparent　electrode,　indium　tin　oxide　(ITO)　film　is　fabricated　by　vacuum　E-beam　evaporation.　The　thermal　annealing　effects　on　the　ITO/GaP　contact　have　been　investigated　by　means　of　the　transmission　line　model　method.　Under　435　°C,　with　rapid　thermal　annealing　for　40　s　in　N2　ambient,　the　ITO　contact　resistance　reaches　the　minimized　value　of　4.3　×　10-3　Ω　cm2.　The　results　from　Hall　testing　and　Auger　spectra　analysis　indicate　that　the　main　reasons　for　the　change　of　the　contact　resistance　are　the　difference　in　the　concentration　of　carriers　and　the　diffusion　of　In,　Ga,　O.　Furthermore,　the　reliability　of　AlGaInP　LEDs　with　a　300-nm　thickness　transparent　conducting　ITO　film　is　studied.　The　increase　of　LED　chip　voltage　results　from　the　degradation　of　ITO　film.　Moreover　the　difference　between　the　thermal　expansion　coefficient　of　GaP　and　ITO　results　in　the　invalidation　of　the　LED　chip.　©　2010　Chinese　Institute　of　Electronics.