We have investigated the structural properties of ZnSe epilayers that were molecular beam epitaxially grown on (001) GaAs substrates with different tilt angles and tilt directions. We measured the properties of the epilayers by x-ray diffraction, transmission electron microscopy, and etch pit density analysis. Tilting the (001) GaAs substrate toward [010] was very effective in reducing the surface defect density of the ZnSe layers, while tilting toward the [110] direction was of no use. We could observe the increasingly two-dimensional nature of the initial growth mode in the (001) GaAs substrate tilted toward [010]. Growth of a 1.8-&mgr;m-thick ZnSe layer on (001) GaAs tilted 4° toward [010] resulted in a very low surface defect density of 1×104 cm−2.Such a low defect density has seldom been obtained in ZnSe, without growing a GaAs buffer layer below the ZnSe layer. ©1997 American Institute of Physics.