A regime for growing high‐quality GaAs/AlGaAs single‐quantum‐well structures by molecular‐beam epitaxy with interruption only at the AlGaAs‐on‐GaAs heterointerface is reported. For 15‐ and 20‐nm‐wide wells the luminescence linewidth is found to be 0.44 and 0.29 meV, respectively. The data are among the lowest values reported to date. Photoluminescence line splitting due to the formation of extended growth islands was not observed.