This letter presents a study of intermixing in ZnSe/ZnCdSe quantum well structures, using repetitive thermal annealing with photoluminescence measurements. An improvement in the optical quality of the samples was found for anneals at temperatures (∼500 °C) for which macroscopic intermixing is not observed. The interdiffusion process of this system was found to be Fickian with no dependence on alloy composition or strain. An activation energy of 2.3±0.2 eV was obtained for the interdiffusion process over a 250 K temperature range and four decades of interdiffusion coefficient.