The possibility of using x‐ray diffuse scattering experiments to investigate the atomic arrangement within the substituted sublattice in III‐V solid solutions has been demonstrated. TheIcwscattering by static composition waves has been separated from Compton and phonon scattering along the 100 direction in reciprocal space for a thick Ga1−xAlxAs (x=0.32) layer grown by liquid‐phase epitaxy. The dependence ofIcwon the scattering angle has given a detailed experimental proof that the Ga and Al atoms are distributed in a random way within the cation sublattice. An exception to this behavior, which is related to a slight (13%) increase ofIcwat the 100 point, is discussed in the light of the pseudochalcopyrite model for the local bonding in III‐V alloys.