By using scanning tunneling microscopy, low-energy electron diffraction, and Auger electron spectroscopy adsorption and reaction of NO on Si(111)7x7 at 860 K and the effect of subsequent annealing to 1230 K have been studied. The latter results are compared with those obtained on a surface which has been heated to 1260 K during NO exposure. In both cases the previously described "8x8" structure has been obtained. At 860 K etching of Si and formation of oxynitride islands are found at the same time. In scanning tunneling microscopy the 8x8 structure appears as a rather regular array of protrusions in a mean distance of 8/3 a(Si). No indications of the previously proposed coincidence lattice structure [A. G. Schrott and S. C. Fain, Jr., Surf. Sci. 123, 204 (1982)] are seen in the scanning tunneling microscopy results.