Embodiments of the present invention generally relate to methods for lowering the dielectric constant of low-k dielectric films used in semiconductor fabrication. In one embodiment, a method for lowering the dielectric constant (k) of a low-k silicon-containing dielectric film, comprising exposing a porous low-k silicon-containing dielectric film to a hydrofluoric acid solution and subsequently exposing the low-k silicon-containing dielectric film to a silylation agent. The silylation agent reacts with Si—OH functional groups in the porous low-k dielectric film to increase the concentration of carbon in the low-k dielectric film.