Spontaneously formed long‐range Al‐rich and Ga‐rich AlxGa1−xAs/AlyGa1−yAs superlattice in (111)A was demonstrated. This was observed by cross‐sectional transmission electron microscopy (TEM) in 0.75 &mgr;m Al0.30Ga0.70As grown on (111)A GaAs substrates at 640 °C. In contrast, none of the above superstructure was observed by TEM on a side‐by‐side grown (100) oriented substrate. 15 K photoluminescence (PL) showed a 31 meV redshift and six times peak intensity enhancement in layers grown on (111)A substrates to that on (100). A reduced long‐range compositional modulation can be achieved by growth at higher temperatures and is shown in the finer and moderately modulating (111)A Al0.40Ga0.60As grown at 700 °C. A 15 K PL linewidth of 17 meV was achieved in 700 °C grown (111)A A0.40Ga0.60As that is the narrowest reported linewidth for (111)A AlGaAs. ©1995 American Institute of Physics.