We demonstrate a technique for growing fine molecular films on a monolayer scale. We achieve layer-by-layer growth under thermally equilibrium condition by precisely controlling the conditions of an ultra-slow deposition technique. This technique is applicable to various kinds of p-type and n-type organic semiconductors and makes it possible to form a hetero-molecular interface (p-n junction) with molecular level flatness. The technique was used to produce a molecular superlattice, which enables the well-controlled design of energy level alignments in organic semiconductors. (C) 2013 Elsevier B.V. All rights reserved.