Heterovalent ZnSe/GaAs(001) interface structure was controlled by preparing various initial surface structures of GaAs(001) and by pre-growth deposition of Zn or Se. It was found that density of stacking faults and other kind of defects in the ZnSe film strongly depended on the interface structure. In order to reduce the defect density, it was important to avoid chalcogenization of GaAs surface and segregation of excess As. A ZnSe film with lowest density of defects was obtained by Zn treatment on the GaAs(001)-(2×4) surface.