The porous hydrogen methyl silsesquioxane films have been successfully synthesized by the incorporation of poly(amidoamine) (PAMAM) which is thermally decomposed to form nanometer-scale voids within the films. A coupling agent was used to prevent the phase separation of the sacrificial material and the matrix by chemically bonding them together. The decomposition behavior of PAMAM was studied in different atmospheres, and it was found that PAMAM degraded more effectively in air than in nitrogen. Atomic force microscopy and transmission electron microscopy micrographs provided information about the structure of the hybrid films, and specular X-ray reflectivity was used to evaluate the density and porosity of the films. A dielectric constant as low as 2.2 was achieved for closed-cell mesoporous film with PAMAM loading of 15 wt %. (C) 2004 The Electrochemical Society.