The ordinary and extra-ordinary dielectric functions of semi-insulating 4H-SiC in the energy range 1.5-4.5 eV are determined by spectroscopic ellipsometry using a recently developed anisotropic incoherent reflection model. This model is further developed to perform rapid birefringence measurements. Below the minimum band gap the dielectric function is extracted using the Sellmeier dispersion relation. The complex dielectric function response above the band gap was extracted and extrapolated using both the Fourouhi and Bloomer and Tauc Lorentz dispersion models.