Anomalous growth of HfAl3 is observed on 400°C annealing of evaporated thin‐film samples consisting of 900 Å aluminum, on 1000 Å hafnium, 6000 Å aluminum and SiO2 substrates. A continuous layer of HfAl3 forms at the aluminum–hafnium interface nearer the surface, but not at the deeper interface. The surface HfAl3 layer then continues to grow, fed by diffusion of underlying aluminum through the intervening hafnium layer. Needlelike precipitates of HfAl3 are formed along the underlying aluminumgrain boundaries. Observations are made by nuclear backscattering,Auger electron spectroscopy, and transmission electron microscopy. Similar behavior is observed in Al–Zr–Al layers.