The microstructure and composition of the interfacial layer between chemically deposited PbSe and GaAs substrates were studied using high-resolution transmission electron microscopy (HRTEM), Auger electron spectroscopy (AES), x-ray photoelectron spectroscopy (XPS) and energy-filtered TEM.The thickness of the interfacial layer varied significantly from direct contact of the film with the substrate to 5 nm in the thickest regions. The results established the presence of a discontinuous, amorphous intermediate layer of Ga 2 O 3 at the PbSe/GaAs interface.