A method of pore generation by supercritical CO2 (SCCO2) and co-solvent extraction for the preparation of nanohybrid film and mesoporous organosilicate thin film for ultralow dielectric constant materials is investigated. The films were treated with SCCO2/methyl ethyl ketone-tetrahydrofuran co-solvent combination and it was found that the treatment produced dielectric constant (k) values of 2.30 for closed-pore and 1.61 for open-pore nanohybrid films; 2.14 for cetyl trimethylammonium bromide-based and 2.50 for polyethylene glycol octadecyl ether-based films. These results suggest that the SCCO2/co-solvent treatment produces closely comparable results with thermal decomposition in terms of Fourier Transform Infrared spectroscopy data, optical constants obtained from variable angle spectroscopic ellipsometry, and k values. (C) 2007 Elsevier B.V. All rights reserved.