Single-crystalline thin films of the homologous series InGaO3(ZnO)(m) (where m is an integer) are fabricated by the reactive solid-phase epitaxy (R-SPE) method. Specifically, the role of ZnO as epitaxial initiator layer for the growth mechanism is clarified High-temperature annealing of bilayer films consisting of an amorphous InGaO3(ZnO)(5) layer deposited at room temperature and an, epitaxial ZnO layer on yttria-stabilized zirconia (YSZ) substrate allows for the growth of single-crystalline film with controlled chemical composition. The epitaxial ZnO thin layer plays an essential role in determining the crystallographic orientation, while the ratio of the thickness of both layers controls the film composition.