Simultaneous measurement of both the conduction‐ and valence‐band dispersion curves in single strained‐layer structures is presented. These measurements rely on the application of recent observations regarding breaking of the usual selection rules for interband magnetoluminescence transitions in modulation‐doped structures. Low‐temperature magneto‐luminescence data for three representative InGaAs/GaAsn‐type single‐strained quantum well structures are presented. For energies approaching 50 meV above the band gap, we find that the conduction band is parabolic with an effective mass of 0.071m0. Over the same energy range, the valence bands are highly nonparabolic.