AbstractA simple numerical method is presented for the calculation of excitonic spectra in real semiconductors like GaAs in intermediate magnetic fields. A proper set of intermediate field functions including nonlinear variational parameters is used for the numerical diagonalization of the exciton matrix with inclusion of the electron‐hole exchange interaction. By the calculation of both the transverse and “longitudinal” levels, a basis is developed for a comparison between theory and experimentally observed splitting pattern in magneto‐reflectivity measurements. A good overall agreement is obtained between theory and experiment in case of GaAs and InP in a region of the magnetic field strength not acceissible up to now neither with low‐field methods nor with the usually adopted adiabatic method in the high‐field case.