Based on the analytical solution of the dispersion equation describing the allowed states in superlattices with thin high barriers, the influence of an electron momentum parallel to the heterojunction boundary on the height of the dimensional subband bottom in such superlattices was estimated for the transistor heterostructures, and, accordingly, the efficiency of those heterostructures located on the channel edges was evaluated. The study has shown that such sets of barriers prevent the transition from a narrow-band transistor channel to a wide-band material confining the channel (at least until intense transitions to the semiconductor upper valleys start in the channel itself). Keywords: superlattice, potential barrier, dispersion equation, transistor heterostructure.