Observation of magneto‐optical transitions in a Si center &dgr;‐doped quantum well is reported. The excitons are stabilized by the application of the field. With photoluminescence excitation spectroscopy (PLE), transitions below the Fermi level are observed. At magnetic fields ≳8 T broadened Landau levels can be seen. The features in the PLE spectra sharpen up significantly when the Larmor diameter becomes less than the average interimpurity spacing. The effect of the ionized donors in the well on the optical spectra is discussed.