High concentration Ge-doped in CZ-Si single crystals were measured by Fourier transform infrared spectroscopy (FTIR) at room temperature (RT) and 10 K together with the SEM-energy dispersive X-ray (EDX) spectroscopy. We make use of the new peak that appears at the wave number of 710 cm(-1). This peak becomes clearer with increasing concentration of Ge, the relation between absorption coefficient (alpha(max)) half-peak breadth (W-1/2) and Ge concentration is determined. And the formulas of determining Ge concentration in CZ-Si single crystals by means of FTIR technology have been given at RT and 10 K. The result of error analysis indicates that FTIR technology is capable of determining the Ge concentration in CZ-Si single crystal. (c) 2005 Elsevier B.V. All rights reserved.