The　reasons　for　low　output　power　of　AlGaInP　Light　Emitting　Diodes　(LEDs)　have　been　analysed.　LEDs　with　AlGaInP　material　have　high　internal　but　low　external　quantum　efficiency　and　much　heat　generated　inside　especially　at　a　large　injected　current　which　would　reduce　both　the　internal　and　external　quantum　efficiencies.　Two　kinds　of　LEDs　with　the　same　active　region　but　different　window　layers　have　been　fabricated.　The　new　window　layer　composed　of　textured　0.5　mu　m　GaP　and　thin　Indium-Tin-Oxide　film　has　shown　that　low　external　quantum　efficiency　(EQE)　has　serious　impaction　on　the　internal　quantum　efficiency　(IQE),　because　the　carrier　distribution　will　change　with　the　body　temperature　increasing　due　to　the　heat　inside,　and　the　test　results　have　shown　the　evidence　of　LEDs　with　lower　output　power　and　bigger　wavelength　red　shift.