We developed a novel cethyltrimethylammonium bromide (CTAB)/commercial name (polyfunctional silaxane network precursor) (TSC-2)/tetraethyl orthosilicate (TEOS)-based precursor solution for the preparation of low-dielectric-constant materials. Thin, solid dielectric films were fabricated by spin-coating this precursor solution on silicon wafers and drying and calcinating the obtained layers. TSC-2 considerably lowered atmospheric water absorption by dielectric films and, hence, their dielectric constant. Additional treatment of dielectric films by the hexamethyl-dysilizane (HMDS) solution in supercritical CO2 effectively decreased moisture absorption by the film, making its dielectric constant even, lower and stable over time. This treatment also made the film mechanical modulus higher.