Reliability of pulsed electron‐beam‐alloyed AuGe/Pt ohmic contacts on GaAs has been studied and compared with thermally alloyed contacts. Electron‐beam‐alloyed contacts have excellent surface morphology and low contact resistance, but are not as reliable as thermally alloyed contacts; the specific contact resistance deteriorates with thermal aging at 250 °C. The degradation is explained by the interdiffusion and compound formation in the metals during aging.