The alkaline fusion method for the analysis of the hydrocarbon portion of poly(dimethyl siloxane) gum stock containing pendant vinyl groups has been applied to systems crosslinked with dicumyl peroxide in the presence of near‐UV radiation. Crosslinks made of butyl and propyl chains both with and without aromatic residues were found. Under the conditions of this study the dicumyl peroxide efficiency as a crosslinking agent is slightly greater than one. Owing to the formation of three carbon‐containing crosslinks, the total chemical crosslink density of the system was greater than predicted from simple vinyl‐to‐vinyl addition.