Intersubband transitions in GaAs/GaAlAs multiquantum wells (QW) under hydrostatic pressure have been investigated with photomodulated transmission spectroscopy and free-standing QW samples. In addition to the direct transitions associated with the &Ggr; critical points, severalL-related transitions between theLconduction band and the &Ggr; valence band of the GaAlAs barriers and between theLconduction subbands and the &Ggr; valence subbands inside the GaAs quantum wells are observed. The distinctL-related spectral features are a clear indication that photomodulated transmission is particularly useful for enhancement of the weak phonon-assisted indirect transitions. ©1997 American Institute of Physics.