We present the results of structural, analytical, optical and electrophysical investigations of TiBx-GaAs contacts. They were obtained by magnetron sputtering from pressed powder targets and were studied before and after rapid (60 s) thermal annealing (RTA) in a hydrogen atmosphere at T = 400 degrees C, 600 degrees C and 800 degrees C. It was shown that a transition layer is formed by GaxB1-xAs phase during contact formation. The decay of this phase during thermal annealing causes a parameter degradation in the surface-barrier diodes.