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β-Iron disilicide (FeSi 2 ) single crystals were grown by the chemical vapor transport (CVT) with iodine (I 2 ) as a transport agent. The optical and electrical properties of the crystals were then studied. Raman spectrum shows a set of strong A g -mode peaks and photoluminescence (PL) spectra show a very broad emission band. In order to study the effect of annealing on the electrical properties, β-FeSi 2 single crystals were annealed in the range of 1073–1213 K for 48 h. The electrical properties of as-grown and annealed crystals were then evaluated by measuring their Hall effects in the temperature range of 10–300 K. The results show that both of the as-grown and annealed single crystals are of the n-type conductivity. The dependences of the temperature indicate that carrier concentration decreases and Hall mobility increases with the increase of measuring temperature. When the annealing temperature reaches above 1223 K, these changes tend to saturation. Furthermore, the donor ionization energies were estimated and the scattering mechanisms of carrier were discussed.