We present an Auger electron spectroscopy (AES) study of the adsorption of nitric oxide (NO) on a clean Si(100)2 × 1 surface at 300 and 550 K. Accurate measurement reeveal well resolved fine structure at Auger SiL2.3VV transitions at 62 and 83 eV. These peaks can be attributed to Si---O and Si---N bonds. Furthermore, it is argued that the broadening in the SiLi2.3VV Auger transition at 83 eV at 300 K may be composed of two nearby peaks, which could be attributed to two different kinds of chemical bonding, Si---N and Si---O. The absence of a peak at 69 eV at room temperature strongly suggests the NO adsorption on a Si(100)2 × 1 surface to be molecular. Dissociation of NO on the Si(100)2 × 1 surface is observed at 550 K.