Carrier transport in ion-beam synthesized (IBS) beta-FeSi2 was investigated by using Hall effect measurement at low temperatures (15-300 K). The measurement showed p-type conduction in the temperature range of 15-300 K. The Hall coefficient increased with increasing temperature up to 25 K, and then it decreased, which suggested the two carrier conduction, i.e., the impurity conduction, as well as the conduction in the valence band, play an important role in the carrier transport. Based on the two carrier model, the hole concentration and mobility for the impurity conduction at 25 K were evaluated to be 9.9 x 10(17) cm(-3) and 0.85 cm(2) V-1 s(-1), respectively, which suggested that the acceptors were isolated and did not form the impurity band at the impurity concentration of 9.9X 1017 cm(-3). Thus, the threshold concentration for the impurity band formation was more than three orders of magnitude higher than that for GaAs (2x 10(16) cm(-3)), which could be explained on the basis of the Mott criterion. (C) 2004 Elsevier B.V. All rights reserved.