The thermal decomposition of alkylsiloxane self-assembled monolayers in air has been studied using atomic force microscopy, X-ray photoelectron spectroscopy, and contact angle analysis. It is found that the monolayers are stable in air up to about 200 degreesC. Above 220 degreesC the monolayers primarily decompose through C-C bond cleavage, with a gradual reduction in chain length. The siloxane headgroups remain on the surface following the decomposition of hydrocarbon fragments in the monolayers.