In this study, dislocation motions in GaN-based materials and devices were quantitatively estimated in order to determine why GaN-based light-emitting diodes have remarkable reliability and longevity in spite of extremely high dislocation density. The dislocation velocity of GaN-based materials was calculated by estimating the activation energy of dislocation, and comparing it with that of GaAs, which are typically used for light-emitting devices. It was estimated that the dislocation mobility of GaN-related materials was lower than that of GaAs by a factor of approximately 10−10–10−16, at room temperature. Furthermore, dislocation velocity under current injection became about 10−20times lower than that of GaAs, under the assumption that the dislocations in GaN-related materials do not act as nonradiative recombination centers. The possibility of degradation under high current densities and high temperature, as would be found in GaN-based laser diodes, is also discussed. ©1997 American Institute of Physics.