The high-temperature stability of Schottky barriers on GaAs has been correlated with the thermodynamic driving force for chemical reaction between the metallic contacts and the substrate. The chemical stability of a gate metallurgy can result in the stability of the electrical characteristics of the contact after high-temperature anneal. Since single element metal contacts on GaAs are chemically unstable, thermally stable Schottky barriers are not expected from these systems. Alternatively, most of the common metal silicides are chemically stable on GaAs and hence are more likely to form Schottky barriers which are stable against high-temperature annealing. The chemically stable silicides of Ni and Co, which exhibit low electrical resistivities, are suggested as improved gate metallurgies in self-aligned metal-semiconductor field-effect transistor technologies.