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The elevated temperature stability of a commercial GaAs enhancement-depletion-mode MESFET process has been characterized; the observations made are relevant to device operation at elevated temperatures, with implications for optoelectronic integration on GaAs integrated circuits by selective-area epitaxial growth, and to long term circuit and device reliability. Although the transistor electrical characteristics are stable for up to five hours at 500/spl deg/C, a metallurgical reaction between the interconnect metal AlCu/sub x/ core and WN/sub x/ claddings has been identified which limits circuits to five hour operation at 470/spl deg/C. This later reaction proceeds with an activation energy of 3.5 eV and results in a 15-fold increase in interconnect metal sheet resistance. A geometry-dependent increase in ohmic contact resistance is seen at somewhat higher temperature which is ascribed to the penetration of aluminum-containing compounds to the ohmic contact edge.