We have carried out structural studies of nonluminescent areas developed by current injection in ZnMgSSe alloy‐based II–VI blue light emitting diodes by electroluminescence topography and transmission electron microscopy. The nonradiative regions, which spread out in the 〈100〉 direction during current injection, consist of a high density of dislocation dipoles and dislocation loops. The source of these defects is the preexisting stacking faults originating at the substrate/epilayer interface. The dipoles themselves are aligned along both of the 〈110〉 directions lying in the {111} plane. Their Burgers vectors were of the type (a/2)〈011〉 inclined at 45° to the (001) junction plane.