This paper presents results on the direct synthesis of the β-FeSi2 phase by ion beam mixing of Fe/Si bilayers with Xe ions. The influence of the substrate temperature, ion fluence and energy on the growth of this phase was investigated using Rutherford backscattering (RBS), X-ray diffraction (XRD) and conversion electron Mössbauer spectroscopy (CEMS). Complete growth of single-phase β-FeSi2 was achieved by 205 keV Xe ion irradiation to a fluence of 2 × 1016 ions/cm2 at 600°C. We propose a two-step reaction mechanism involving thermal and ion beam energy deposition. © 2001 Elsevier Science B.V.