We performed a comparative investigation of interface structure and composition in pseudomorphic ZnSe∕GaAs(001) heterostructures grown using interface fabrication procedures that produce epilayers with minimum stacking fault densities (below 104cm−2). We detected in all cases a 1nm thick intermixed region at the interface that is depleted of As and is comprised of a (Zn,Ga)As alloy with zincblende structure. No ZnAs formation was found in any of the interfaces examined. Our results imply that Ga-Se reactions at the ZnSe∕GaAs interface do not necessarily lead to nucleation of high densities of stacking faults and that ZnAs formation plays no role in the observed reduction of the native defect density.