We present an analysis of optical data from ZnSe strained‐layer quantum wells surrounded by Zn1−xMgxSySe1−ybarrier layers to extract the band offsets. If we use only the ground state transitions from our experimental data, no unique value of the offset can be obtained: a direct consequence of the fact that there are no uniquely agreed upon values of the effective masses for ZnSe available. However, if we include the excited states, only one out of six considered sets of effective masses gives a reasonable fit to the experimental data, giving the conduction band offset of only 10% of the band gap difference. ©1995 American Institute of Physics.