High resolution core level photoemission spectroscopy has been used to obtain the first direct identification of the chemical species remaining on silicon surfaces after exposure to fluorine. Both Si(111) 2×1 and Si(111) 7×7 were exposed to fluorine via the dissociative chemisorption of XeF2. For fluorine coverages in the monolayer regime, SiF1, SiF2, and SiF3were all present although their relative abundance varied significantly between the two surfaces. No evidence for the existence of unreacted interestitial fluorine was found. These results suggest the need for modification of current models describing plasma and reactive ion etching of silicon.