Effects of a ZnSe buffer layer for heteroepitaxial growth of GaAs layers on CaF2 layers were investigated. It was found that wettability of ZnSe was better than that of GaAs on the CaF2(111) layer through the contact angle measurement of the ZnSe and GaAs islands by an atomic force microscope (AFM). It was found by secondary ion mass spectrometry (SIMS) measurement that a ZnSe buffer layer suppressed diffusion of Ca and F into the GaAs layer which was found in the case of direct growth and produced an abrupt interface between the CaF2 layer and GaAs layer. Analysis of the initial stages of GaAs growth revealed that nucleation density was increased and crystallinity was better when the ZnSe buffer layer was grown on the CaF2 surface. It is considered to contribute to better crystallinity of GaAs layers in the subsequent growth.