The electronic properties of both symmetric and asymmetric with respect to the geometric dimensions of the semiconductor structure layers have been studied. In this case, the Schrödinger equation is solved both for the general wave function and for quantum wells, taking into account the difference in effective masses in the layers of the structure. The expression for the gap between the energy levels of the energy appearing in the quantum well is analyzed. It is shown that the energy gap is determined by a quantity that is a measure of the asymmetry of two quantum wells, and it is equal to zero for symmetric wells. In the case when the asymmetry of the wells is negligibly small, then the gap between the levels in the tunnel-coupled wells is determined by the value characterizing the tunneling splitting of the energy levels. It is determined that in tunnel-coupled wells, the energy levels are shifted relative to the levels of isolated wells, and wave functions arise from the wave functions of isolated wells as a result of their mixing.