Better radiation resistance of InP-based solar cells such as InGaP and InGaAsP cells, and minority-carrier-injection-enhanced annealing phenomena of radiation-induced defects in those materials previously found by the authors has been analyzed by considering introduction rates and annealing behavior of radiation-induced defects in InP-related materials. Radiation resistance of InP-related materials is found to be explained by lower damage coefficients and band-gap energy effects on solar cell degradation compared to other materials. (C) 2002 Published by Elsevier Science B.V.