After preparing cobalt silicide layers on arsenic-doped silicon substrates using capping layers, such as Ti and TiN thin films, the behavior of surface oxidation was investigated under rapid thermal oxidation (RTO) conditions. The type of capping layer was found to affect the oxidation of the cobalt silicide. Oxide grew faster on the cobalt silicide prepared with the Ti capping layer than on the TiN capping layer under the same RTO conditions. The difference in growth rate was caused by the relatively high outdiffusion of arsenic dopants from the silicon substrate to the cobalt silicide prepared with the Ti capping layer.