It is shown that in some cases of the metal‐insulator‐semiconductor systems the electron tunnel current may be expressed in the form of one‐dimensional integral with modified ‘‘supply function’’ even if the effective mass is not the same in each region of the system. The proposed formula together with description of the semiconductor space charge region (which is not considered in the paper) may be used for modeling of the electron tunnel current‐voltage characteristics, e.g., of the metal–SiO2–Si⟨100⟩ tunnel diodes. The considerations are based on the electron total energy and transverse wave‐vector conservation assumptions.