A method of determining a temperature in a deposition reactor includes the steps of depositing a first epitaxial layer of silicon germanium on a substrate, depositing a second epitaxial layer of silicon above the first epitaxial layer, measuring the thickness of the second epitaxial layer and determining the temperature in the deposition reactor using the measured thickness of the second epitaxial layer. The method may also include heating the deposition reactor to approximately a predetermined temperature using a heating device and a temperature measuring device and generating a signal indicative of a temperature within the deposition reactor. The method may also contain the steps of comparing the measured thickness with a predetermined thickness of the second epitaxial layer corresponding to the predetermined temperature and determining the temperature in the deposition reactor using the measured thickness of the second epitaxial layer and the predetermined thickness of the second epitaxial layer.