Characteristics of decanethiol and 1,4-benzenedimethanethiol (p-BDMT) self-assembled monolayers (SAMs) grown using solution and vapor techniques were studied with X-ray photoelectron spectroscopy (XPS) and in-plane resistivity measurements. Self-assembled monolayers of decanethiol show nearly identical coverages for samples grown from solution and from vapor. Films of p-BDMT grown from solution show monolayer packing densities similar to those of alkanethiols, as indicated by the surface thiolate concentrations. A much different result is obtained for p-BDMT SAMs when grown from vapor. A monolayer packing density that is 12-16% higher than that of alkanethiols is observed with XPS and in-plane resistivity measurements. It is also shown that p-BDMT forms multilayers when SAMs are grown by both solution and vapor techniques.