Electrical studies of W/n‐GaAs Schottky diodes have shown that aging at 350 or 500 °C does not significantly change the forwardI‐Vcharacteristics of the diodes. Using4He+backscattering analysis, it is shown that the W/GaAs interface of simulated diodes does not exhibit any evidence of interdiffusion or reaction. By contrast, considerable alloying occurs in both Au/GaAs and Pt/GaAs systems. In the former, Ga outdiffuses to the surface of Au and Au diffuses into GaAs upon aging at 250 or 350 °C; this has the effect of decreasing the barrier height &phgr;Bfrom 0.9 to [inverted lazy s] 0.6 V and increasing the ideality parameternfrom 1.0 to [inverted lazy s] 1.2. Interdiffusion in the Pt/GaAs couples, aged at 500 °C, results in the formation of a layered arrangement of type PtGa/PtAs2/GaAs. The PtAs2/n‐GaAs interface is associated with a slightly higher &phgr;B([inverted lazy s] 0.89 V) than that found for the Pt/n‐GaAs interface (&phgr;B[inverted lazy s] 0.84 V).