Gel to glass transformation of methyltriethoxysilane was investigated using infrared and Raman spectroscopies. The vibrational frequencies of the Si-O network are found to be a sensitive probe of the gel to glass transformation, which is measured to be at ca. 950 degrees C for this system, under the experimental conditions used for the synthesis. Vibrational data are also compatible with an earlier suggestion of the presence of polyhedral silsesquioxanes type structures embedded in a 3-D network. Further evidence is presented for the formation of Si-CH2-Si and Si-C2H4-Si units during the pyrolysis process.