A heterostructure, consisting of two GaAs quantum wells each of 40 A˚ width separated by a 40‐A˚ Al0.5Ga0.5As barrier, has been grown by molecular beam epitaxy and examined optically for Al‐Ga disorder (alloy clustering). The photoluminescent and excitation spectra showed no evidence of clustering, in marked contrast to results on a similar structure grown by metal‐organic chemical vapor deposition. Thus any clusters present must be less than 40 A˚ in diameter. The spectra also support an island‐like interface with steps of ∼one monolayer in height and ≳300 A˚ in lateral extent.