The implementation of silicon germanium (SiGe) and silicon germanium with substitutional carbon incorporation (SiGe:C) in BiCMOS and CMOS technologies requires very good control of epitaxial layer thickness and layer composition. In contrast with most of the characterization methods, spectroscopic ellipsometry (SE) allows a fast, inline and non-destructive analysis, including fast wafer mapping facilities. In this paper, the existing SE measurement routine for SiGe is extended to SiGe:C with substitutional carbon (C) incorporation. The optical dispersion is described by means of the harmonic oscillator model. The extraction of the C content is based on a well-defined shift of the resonant energy of the first oscillator. The SE system is a small spot (28×14 µm2) spectroscopic ellipsometer, which allows the characterization of epitaxial SiGe and SiGe:C layers grown on patterned wafers, while this small window size prevents measurements by RBS. The SE technique is therefore a very powerful tool for optimization of the layer uniformities in both thickness and composition.