The reaction of Si (100) with C2H4from a molecular beam source has been studied using x‐ray photoelectron spectroscopy, electron‐energy‐loss spectroscopy, and Auger spectroscopy. Using these methods, we have studied the kinetics of SiC formation under conditions wherenogas‐phaseexcitationprocessescan contribute. At Si (100) temperatures below 940 K, a ‘‘Si‐C alloy’’ forms on the surface; annealing to higher temperatures produces SiC exhibiting electron spectroscopic properties identical to SiC (0001). By studies of the characteristic bulk‐ and surface‐plasmon‐loss features in the SiC thin film, it has been shown that surface aggregation of bulk Si on top of the growing SiC film occurs atT≥940 K. Under optimum SiC growth conditions, C2H4yields about 2×10−3SiC units per C2H4surface collision on Si (100).