A new diagnostic technique was used to examine the alloying behavior of the Ni/Au&sngbnd;Ge Ohmic contact ton‐type GaAs. By combining Auger electron spectroscopy with sputter etching, depth‐composition profiles of Ni, Au, Ge, Ga, and As were obtained for alloyed and unalloyed samples. Gallium out‐diffusion and surface accumulation during alloying was observed. The degree of Ga out‐diffusion as well as the redistribution of Ga and As in the alloyed region was found to depend on the orientation of the GaAs substrate. It was shown that the overlaying Ni film does not cover the Au&sngbnd;Ge uniformly during alloying.