Low‐temperature (1.8 K) photoluminescence spectra of a Ga0.52In0.48P–(Al0.58Ga0.42)0.52In0.48P multiple quantum well have been measured as a function of hydrostatic pressure from 0 to 5.0 GPa. The extrapolation to zero pressure of the energy of the indirectk‐and‐real‐space barrierXto well &Ggr; transition allows the direct determination of the valence band offset for this heterojunction system. A value of &Dgr;Ev=(0.35±0.05)&Dgr;Egis found, in good agreement with values previously determined from the theoretical modeling of quantum well transition energies. ©1995 American Institute of Physics.