The results of analytical (Auger electron spectroscopy, secondary ion mass spectrometry), photoluminescence, spectral ellipsometry and electrophysical investigations of the TiB x –GaAs Schottky contacts are presented. The contacts were obtained by magnetron sputtering and then were thermally annealed in hydrogen atmosphere at T= 400°C, 600°C and 800°C. It was shown that decay of the Ga x B 1−x As phase in a transition layer at the interface during thermal annealing decreases its optical conductivity and causes degradation of the surface-barrier diodes.