The diffusivity of the zinc Ga1−xAlxAs at 650 °C was studied using sealed‐ampoule diffusion. Whereas Ageno, Roedel, Mellen, and Escher [Appl. Phys. Lett.47, 1193 (1985)] found dramatic decreases in the zinc diffusivity atxAl≊0.05 andxAl≊0.20 using open‐tube diffusion, the results of the present study show that the sealed‐ampoule technique results in a more uniform dependence of the zinc diffusivity on aluminum concentration.