Soft x‐ray photoemission has been utilized to investigate the chemisorption and subsequent reaction of diethylsilane on Si(111) and (100) surfaces. We show that diethylsilane chemisorbs dissociatively to form Si‐CH2CH3surface species on Si(111) and Si(100) at room temperature. These species are identified by two very sharp peaks observed in the valence band spectra of both surfaces, positioned at 17.9 and 14.3 eV binding energy. Si 2pand C 1score level spectra were measured following exposures of Si(100) and (111) substrates as a function of surface temperature. C 1sdata 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 –CH2CH3ethyl groups are observed on the surface at room temperature, these species appear to partially dehydrogenate above 300 °C producing a mixture of –CH2CH3groups and other intermediate carbonaceous species. At a growth temperature of about 400 °C for the technologically important (100) surface, 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 candidate for SiC formation by chemical vapor deposition techniques.