The efficiency droop behavior of GaN-based light emitting diodes (LEDs) is studied when the LEDs are under reverse-current and high-temperature stress tests respectively. It is found that reverse-current stress mainly induces additional non-radiative recombination centers within the active region of InGaN/GaN multiple quantum wells, which degrade the overall efficiency of the GaN LED under test but push the peak-efficiency-current towards higher magnitude. The up-shift of peak-efficiency-current can be explained by a rate-equation model in which the newly-created defects by reverse-current stress enlarge the dominant low-current region of non-radiative recombinations. Comparatively, high-temperature stress mainly increases the series resistance of the LED under test. Although the overall efficiency of the GaN LED also drops, there is no shift of peak-efficiency-current induced by the high-temperature stress. (C) 2010 Elsevier Ltd. All rights reserved.