Soft x-ray synchrotron radiation has been utilized as the excitation source in a high-resolution photoemission experiment designed to investigate the chemisorption and subsequent reaction of diethylsilane on the technologically important Si(100) surface. We have found that diethylsilane chemisorbs dissociatively to form Si-CH2CH3 surface species on Si(100) following a room temperature exposure. These species are identified by two very sharp peaks observed in the valence band spectra positioned at 17.9 and 14.3 eV binding energy. In addition, C Is core level spectra, measured following exposures of Si(100) substrates as a function of surface temperature, show that carbon, in some form, exists on the Si surface following exposures at every temperature from room temperature to about 600°C. While only -CH2CH3 ethyl groups are observed on the surface at room temperature, these species appear to partially dehydrogenate at 300°C, producing a mixture of -CH2CH3 groups and other intermediate carbonaceous species. At a growth temperature of about 400°C the intermixing of elemental carbon with Si begins. At higher temperatures, we observe the continued degradation of diethylsilane to produce a Si + C alloy on the surface at 600°C. Our results indicate that diethylsilane has potential as a molecular precursor for SiC formation by chemical vapor deposition techniques.