Abstract Direct preparation of non-doped, and Ru- or Ge-doped β-FeSi 2 films from the gaseous phase have been studied using a ternary simultaneous electron beam deposition apparatus so as to clarify the effect of these doping elements on the thermoelectric properties and electric conductivity of β-FeSi 2. Substitution of Ru for Fe in β-FeSi 2 up to approximately 7 at.% of Ru seemed to be possible from the X-ray diffraction pattern. On the other hand, substitution of Ge for Si as small as 1.4 at.% Ge brought about the segregation. This feature was also clearly observed in scanning electron micrographs. Therefore, Ru could be successfully doped in β-FeSi 2, however, Ge could not. Though the Seebeck coefficient of β-FeSi 2 has been slightly decreased by doping of Ru, its electric conductivity has been increased by one order of magnitude.