A theoretical method for calculating the variation of optical transition energyEg,optin semiconductors with heavyndoping is presented. The calculations based on the Moss–Burstein shift and band‐gap shrinkage take into account both exchange and Coulomb interactions, the latter being calculated for nonparabolic bands. A comparison with the experimental values ofEg,optfor heavilyn‐doped GaAs and InP shows good agreement over wide ranges of temperature and doping and can satisfactorily explain photoluminescent emission at energies up to 1.65 eV in GaAs (1.8 °K) and 1.91 eV in InP (300 °K).