A model for determining the critical thickness of a film hc is developed to introduce misfit dislocations in the slip planes of a film and a substrate parallel to the interphase boundary (111). Experimental values hc that agree with calculated values are determined for the Ge/Si(111) and Si3N4/Ge(111) heterosystems. The two-level epitaxial growth of Ge on Si is attained in the regime of combining the step-layer and 2D island growth mechanisms.