By combining reflectance spectroscopy and spectroscopic ellipsometry, the complex dielectric function of SrTiO3 in the frequency range 40–5000 cm-1 at 20, 100, 200, and 300 K has been determined. Using a factorized description, analytical expressions for the optical quantities were derived, giving excellent agreement with the experimental data. These can be used for two‐layer fits of films on SrTiO3, e.g., of high‐Tc superconductors. The fit parameters complement very well those found at higher temperatures. © 1995 American Institute of Physics.