beta-FeSi2 films were prepared on Si(001) substrates by the molecular beam epitaxy method using an Fe source. The crystallinity and crystallographic orientation of beta-FeSi2 films on Si(001) substrates were characterized by using X-ray diffraction. Optical constants and the onset of the absorption edge of beta-FeSi2 films on Si(001) substrates were evaluated by solving simultaneous equations of reflectance and transmittance data. The extinction coefficient calculated by the simultaneous equation method showed abrupt absorption onset near the band-edge of beta-FeSi2. (c) 2007 Elsevier B.V. All rights reserved.