[en] We present a theory for heterostructures based on diamond structured semiconductors, with an emphasis of calculating inter-valley coupling. The theory allows taking into account microscopic symmetry of heterointerface within the envelope-function approach. To find out corrections to the effective Hamiltonian we use methods of group theory. We calculated valley-orbit splitting and electron wave functions for SiO₂/Si/SiO₂ finite square quantum wells. The results are in good agreement with those obtained by other authors