GaAs/AlGaAs quantum wells (QWs) were grown on (411)A-oriented GaAs substrates by molecular beam epitaxy (MBE). Photoluminescence linewidths at 4.2 K are almost the same as the narrowest linewidths reported so far for GaAs/AlGaAs QWs grown on (100)-oriented GaAs substrates with the growth interruption at the heterointerfaces. Furthermore, only one sharp peak was observed for each QW on the (411) substrate over the whole area of the wafer (10 mm X 10 mm), in contrast with three splitted luminescence peaks for one kind of GaAs/AlGaAs QW grown on the (100) substrates by MBE with growth interruption. This result implies that effectively atomically flat interfaces over a macroscopic area (about 10 mm X 10 mm) has been realized for the first time in GaAs/Al0.3Ga0.7As QWs grown on (411)A GaAs substrates by MBE. This is possibly due to the large migration of Ga and Al atoms on the (411)A plane during MBE growth and the step-flow growth mode on the atomically corrugated (411)A plane.