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The infrared reflectance spectra of both 4H-SiC substrates and epilayers are measured in a wave number range from 400 cm-1 to 4000 cm-1 using a Fourier-transform spectrometer. The thicknesses of the 4H-SiC epilayers and the electrical properties, including the free-carrier concentrations and the mobilities of both the 4H-SiC substrates and the epilayers, are characterized through full line-shape fitting analyses. The correlations of the theoretical spectral profiles with the 4H-SiC electrical properties in the 30 cm-1-4000 cm-1 and 400 cm-1-4000 cm-1 spectral regions are established by introducing a parameter defined as error quadratic sum. It is indicated that their correlations become stronger at a higher carrier concentration and in a wider spectral region (30 cm-1-4000 cm-1). These results suggest that the infrared reflectance technique can be used to accurately determine the thicknesses of the epilayers and the carrier concentrations, and the mobilities of both lightly and heavily doped 4H-SiC wafers. [ABSTRACT FROM AUTHOR]