Clean Si(111) surfaces were thermally nitrided at various temperatures by exposure to low pressures (1×10−6 Torr) of NO in a UHV system. The nitridation process was monitored by multiple surface analytical techniques including AES, XPS, UPS, LEED, and thermal desorption. At substrate temperatures below 800°C a silicon oxynitride was formed in which the nitrogen to oxygen ratio increased with increasing reaction temperature. These oxynitride films were converted to nitride films by loss of O and SiO when heated to temperatures greater than 850°C in vacuum. Exposure of the clean Si to NO at temperatures greater than 1000°C produced an oxygen‐free nitride film. The nitride films formed by either route gave the ’’doublet’’ LEED pattern which has previously been associated with the formation of a two domain epitaxial α‐Si3N4 layer. Due to the high reactivity of NO, the presence of 20%–30% C on the Si surface was not necessary for nucleation sites as had been reported for nitridation by NH3.