This paper demonstrates the molecular beam epitaxial growth of metallic full-Heusler Ni2TiSn precipitates within semiconducting NiTiSn host matrix, and discusses the structural and chemical stability of this biphasic epitaxial composite and its influence on the electronic properties. Structural properties of the epitaxial films were characterized by in-situ reflection high-energy electron diffraction and ex-situ by X-ray diffraction and transmission electron microscopy. The results indicate the presence of a secondary phase with full Heusler ordering within half-Heusler host matrix. Both the parent half-Heusler and the secondary full-Heusler phases in the epitaxial films are strained from their bulk lattice parameters. Electronic properties show an increase in resistivity at low Ni excess. (C) 2017 Elsevier B.V. All rights reserved.