Thin films of polycrystalline beta-FeSi2 were grown on (100) Si substrates of high resistivity by electron beam evaporation of Si/Fe ultrathin multilayers and subsequent annealing by conventional vacuum furnace (CVF) and rapid thermal annealing (RTA) for 1 h and 30 s, respectively, in the temperature range from 600 to 900 degrees C. X-ray diffraction, Raman spectroscopy, spectroscopic ellipsometry, resistivity and Hall measurements were employed for characterization of the silicide layers quality in terms of the annealing conditions. For the silicide layers prepared by CVF annealing, although the grain size increases with increasing the annealing temperature, the optimum temperature to obtain the higher material quality (carrier mobility of the order of 100 cm(2) Vs(-1) and carrier concentration of about 1 X 10(17) cm(-3)) is about 700 degrees C. At higher annealing temperatures, the quality of the material is degraded due to the presence of the oxide Fe2O3. In the case of the silicides prepared by RTA, the quality of the material is improved progressively with increasing the annealing temperature up to 900 degrees C.