In highly excited semiconductor systems near the transition from direct to indirect band structure (cross-over) the energetic distance between different conduction band minima is a nonmonotonous function of the excitation intensity. A theoretical explanation of this experimental result is given. Our investigations are based on the evaluation of photoluminescence spectra using a careful lineshape analysis. The nonmonotony is a consequence of the unequal shrinkage of the direct and indirect gaps as a function of the population of energetically comparable conduction band valleys in a material near cross-over. In the situation discussed an optical switching mechanism is expected, which is explained with special respect to its switching time. Important problems of electron-electron interaction are discussed.