Electroreflectance measurements have been performed on GaAs/Ga1-xAlkAs single and multiple quantum well samples for GaAs well widths of 100 Ǻ. The electric field is applied perpendicular to the well using a pin diode arrangement or a semi-transparent Schottky barrier. Sharp features are observed in spectra measured both at room and at helium temperatures (15 K) at energies corresponding to transitions between heavy- or light- hole quantum well levels associated with the valence band and electron levels associated with the conduction band. Comparison is made between the energies of optical transitions measured by electroreflectance and by complementary photoluminescence emission and excitation spectroscopy. The energies of optical transitions are observed to decrease with increasing DC electric field at the well and a resonance model has been developed to explain the observed shifts.