We investigated solid-phase growth reactions for the fabrication of β-FeSi₂ films from Fe and FeSi sources by reflection high-energy electron diffraction (RHEED). To enhance the interdiffusion of Fe and Si for the growth of β-FeSi₂, the use of FeSi instead of pure Fe as the source for the initial deposition was examined. The RHEED observation during the solid phase reaction indicated that the growth temperature was markedly decreased to 390K using the FeSi source. We discuss the reaction mechanism of the solid phase growth of β-FeSi₂ from Fe and FeSi sources in this paper.