A method to control the hydrophobicity and dielectric constant of mesoporous silica films for ultralow-k applications is described. Several surfactants have been used as sacrificial materials in (organo)silicate matrixes, prepared from tetraethoxysilane and methyltrimethoxysilane. To elucidate the relation between the composition of the films and their structure, the synthesis, chemical composition, mechanical properties, pore structure, crystallinity, and dielectric constant of the films were investigated. The high extent to which organic groups can be incorporated in these thin films opens the possibility to obtain a fully hydrophobic surface. Further, a combination of tetraethoxysilane and methyltrimethoxysilane leads to dense matrixes. The film properties were optimized for low-k applications by varying the processing conditions. Films containing 50-60% methyltrimethoxysilane in tetraethoxysilane and cetyl trimethylammonium bromide as a surfactant appear most attractive as a low-k material. These films are hydrophobic, have a dense matrix, and exhibit the smallest pore sizes (similar to3 nm), which may facilitate integration issues.