This paper investigates a novel approach for accurate refinement and direct determination of dielectric properties of uniaxial materials below the gap, available both in form of a thick transparent double side polished wafer, and as a semi-infinite bulk wafer (single side polished). Most of the common hexagonal and trigonal wide band gap materials are uniaxial birefringent. We propose to split the complete accurate characterisation of the optical properties of these materials into several steps, using spectroscopic ellipsometry. The overall goal is thus to determine both the ordinary and extra ordinary components of the dielectric function. The birefringence is determined from a double side polished wafer. A spectroscopic fit is further used to determine the overlayer (oxide) thickness and approximate dielectric functions, while we show that higher sensitivity to the ordinary dielectric function may be obtained through the Brewster angle condition obtained from spectroscopic ellipsometry. The material under investigation in the current paper is 4H-SiC.