We report on optical characterization of epitaxially grown SiGe heterojunction bipolar transistor (HBT) structures. Using a commercially available system with non-invasive optical techniques such as, spectroscopic ellipsometry and near normal angle of incidence reflectometry, we have established excellent repeatability and accuracy for product development and manufacturing crucial processes. Germanium content of the buried SiGe spacer layers was determined using the Bruggeman effective medium approximation, as well as an alternative method utilizing a linear interpolation of optical spectra. The optical techniques are also used to monitor responses of different deposition factors on structural properties of the material. For example, a kinetically induced island formation phenomenon is investigated and addressed by optimizing the deposition parameters. Comparison of the optically measured germanium depth profile with SIMS showed good agreement. Optical measurements agreed to within 3.7% of the values obtained by SIMS. These results demonstrate that optical measurements are possible for ex situ monitoring of the epitaxial growth production process for high performance SiGe HBT structures. (C) 2003 Elsevier Science B.V. All rights reserved.