Oxide desorption, homoepitaxial m-V buffer growth and the subsequent metalorganic vapor phase epitaxy of ZnS layers on GaP(001) and ZnSe layers on GaAs(001) were monitored in situ at 350 degrees C using reflectance anisotropy spectroscopy and spectroscopic ellipsometry. Thermal oxide desorption in a II-VI reactor without stabilization by a group V partial pressure leads to rough III-V substrate surfaces with a group VI termination. Application of a proper stabilization induces a well-defined c(4 X 4) and a (2 x 1) surface reconstruction on GaAs and GaP, respectively. Atomic force microscopy proves the formation of smooth surfaces with monoatomic steps. Growth of II-VI epilayers was started under various conditions. Anisotropies of the dielectric function that originate from the II-VI surface or from the buried II-VI/III-V interface were calculated from the reflectance spectra. The separated contribution of the interface to the dielectric anisotropy is distinctly affected by different growth starts particularly for ZnS epilayers on Gap.