In order to understand the physical principles which underlie the formation of metal/semiconductor interfaces, epitaxial Al films are grown by molecular beam epitaxy on As‐stabilized and Al‐stabilized AlAs(001) surfaces some of which were coated with a single monolayer (1 ML) of Ga or In. Reflection high‐energy electron diffraction and x‐ray diffraction measurements reveal that the growth direction and epitaxial relationship of the Al films are drastically changed by the surface modification by 1 ML Ga or In. A variety of Al film configurations are obtained, of which the Al(001)/Ga(or In)/AlAs(001) heterostructure is technologically important because it has an ideally lattice matched metal/semiconductor heterostructure. We propose structural models for three Al phases, i.e., Al(001) and two kinds of Al(110), and discuss the physical origin of the variation of Al phases. It is shown that the changes observed in the epitaxial relationships of Al films can be systematically explained in terms of bond strengths at the interface. In the growth of metals on semiconductors, interface modification is shown to be effective for controlling the growth.