We have developed an experimental technique for accurately determining energy‐band offsets in semiconductor quantum wells (QW) based on the fact that the magnitude of the ground‐state light‐hole (LH) energy is more sensitive to the depth of the valence‐band well than is the ground‐state heavy‐hole (HH) energy. In a lattice‐matched, unstrained QW system, this behavior causes the energy difference between the LH and HH excitons to go through a maximum as the well width,Lz, increases from zero. Calculations show that the position, and more importantly, the magnitude of this maximum is a sensitive function of the valence‐band offset,Qv, the parameter which determines the depth of the valence‐band well. By usingQv, or alternativelyQc=1−Qv, as an adjustable parameter and fitting experimentally measured LH‐HH splittings as a function ofLz, an accurate determination of band offsets can be derived. However, we further reduce the experimental uncertainty by plotting LH−HH as a function of HH energy (which is, itself, a function ofLz) rather thanLz, since then all of the relevant data values can be precisely determined from absorption spectroscopy alone. Using this technique, we have derived the conduction‐band offsets for several material systems, including lattice‐mismatched systems and, where a consensus has developed, have obtained values in good agreement with other determinations.