Abstract Semiconducting β-FeSi 2 was grown on Si(0 0 1) substrates by depositing Fe layers of thickness 2, 4 and 6 nm at room temperature in an ultra-high vacuum system and subsequent in situ annealing at 600 °C for 15 min. The phase of the grown polycrystalline β-FeSi 2 was confirmed by electron diffraction and infrared reflectance measurements. Transmission electron microscopy analysis has shown that the structure of the formed β-FeSi 2 is thickness dependent. For an Fe layer of thickness 2 nm, β-FeSi 2 nanodots with a mean diameter of about 15 nm were grown, together with islands of irregular shape and linear or S-type arrays of β-FeSi 2 nanodots. For thicker Fe layers, the grown β-FeSi 2 consisted of continuous polycrystalline layers.