FeSi2films grown in ultrahigh vacuum on Si (111) substrates by solid phase epitaxy (SPE) have been characterized by severalinsituandexsitustructural techniques: reflection high‐energy electron diffraction (RHEED), x‐ray diffraction (XRD), and Rutherford backscattering (RBS). The results on a film a few hundred angstroms thick confirm that the FeSi2which forms in these conditions is the semiconducting β phase and that an epitaxial growth takes place with the (202) and/or (220) FeSi2planes parallel to the Si (111) planes. The lattice mismatch measurements in films as thin as 100 Å indicate that the films are little or no elastically strained, at least at a FeSi2growth temperature of 600 °C.