A thin film of nanocrystalline ZnSe was deposited on GaAs by a chemical method and the resulting heterostructure was characterized for its passivating behavior. A remarkable enhancement in the intensity of photoluminescence of GaAs at 875 nm was achieved as a consequence of the deposition. The passivating effects of nanocrystalline ZnSe was confirmed by thermally stimulated exoelectron emission spectroscopy, a surface technique for gap state analysis. The disappearance of the peak related to the pinned Fermi level position at 0.92 eV below the conduction band edge was the resulting feature. A nanocrystalline growth of ZnSe was observed on GaAs by scanning electron microscopy.