The relationship between the reliability of GaN LEDs and their junction temperatures and ideal factors is investigated. 20 groups of both blue and white GaN LEDs are tested. Their ideal factors and junction temperatures under 700mA operating current are measured. The measurement methods are introduced. After the measurement, 700mA high current accelerated life test is carried out on the LEDs. Analysis results show that the reliability of the LEDs is strongly dependent on their junction temperatures and ideal factors. For most of the unreliable LEDs with their 50% ALT life less than 400 hours, their ideal factors are higher than 10, or the junction temperatures of the blue LEDs under 700mA are higher than 130°C, and the junction temperatures of the white LEDs under 700mA are higher than 120°C.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.