Quantum wells of GaAs lattice matched to GaP have been studied by photoluminescence and electroreflectance. The quantum well thickness was varied between 1 and 6 monolayers in steps of 1 monolayer. Electron-hole transitions have been observed involving states both in theXband and in the&Ggr;band, which have been modeled using a k.p. model in conjunction with the envelope function approximation. Overall agreement between theory and experiment is found using an unstrained valence band offset of 0.6 eV. ©1997 American Institute of Physics.