Low‐temperature photoluminescence excitation spectra of disordered Ga0.5
P quantum wells lattice matched to (311)B
GaAs substrates have been measured for the first time. Transition energies calculated with a
approach agree with experiment within 3 MeV, over the entire range of quantum well thicknesses (Lz
=11–109 Å). A conduction‐band discontinuity of 0.65±0.05 is derived.