Amorphous Ta93Cu7and Ta80Cu20alloy films are prepared by co‐sputtering of pure Ta and pure Cu targets with a rotating sample holder table. To investigate the possible application of these materials as diffusion barriers for the Au‐GaAs system, vacuum annealings are made in the temperature range from 200 to 800 °C. Resistivity change, x‐ray diffraction, and Auger electron spectroscopy measurements are performed to find the chemical and metallurgical stabilities of these materials in this system. The reaction temperature for TaxCu1−xin contact with GaAs lies between 500 and 700 °C. For Au in contact with TaxCu1−xthe reaction occurs at about 600 °C. Amorphous Ta93Cu7shows different interdiffusion characteristics with surrounding elements than does Ta80Cu20.