Abstract Data are presented on the interdiffusion between constituent atoms in multiple layer structures of wide band gap materials grown by MOCVD on to GaAs substrates. The systems ZnS/ZnSe, CdS/ZnS and CdSe/ZnSe have been used as the vehicles for this study. The results obtained suggest that with a common group II element, interdiffusion between the group VI atoms is negligible but that with a common group VI element some evidence exists for interdiffusion on the group II site. The implications of these findings upon device structures are discussed.