We report on comparative photoluminescence (PL) studies of GaAs/Al0.33Ga0.67As single quantum well structures grown via molecular beam epitaxy underidenticalgrowth conditions employing (a) customary practice ofnogrowthinterruptionand (b)growthinterruption. The growth conditions themselves are chosen to be near optimum, as determined from the growth kinetics exemplified by the reflection high‐energy electron diffraction intensity dynamics. Results show PL lines with fine structure and widths among the narrowest ever reported for 28.3 and 56.6 A˚ wells. The fine structure is indicative of kinetically controlled interfaces with a predominant step height of one atomic layer and the linewidths a first measurement of intrinsic alloy disorder scattering.