For the application of SiO2 aerogel film to GaAs based devices, the changes of interfacial chemical bonding state of HCl-cleaned (or S-passivated) GaAs surface were investigated using monochromatic X-ray photoelectron spectroscopy after immersing the GaAs in each constituent of SiO2 sol. A large amount of oxide was formed on the HCl-cleaned GaAs after the treatment using tetraethoxysilane and de-ionized water due to hydroxyl group in SiO2 sol, while the S-passivated GaAs was not oxidized. The interfacial surface of GaAs was also investigated after the removing SiO2 aerogel film formed by supercritical drying. The aerogel film showed 80% of porosity and low dielectric constant of 1.8. Normally the oxidation of GaAs was successfully suppressed with S-passivation, however during the supercritical drying due to the high temperature and pressure, S-passivation layer was completely decomposed, and GaAs-oxides and elemental As were generated somewhat, but less than the case of HCl-treated GaAs. Furthermore, the formation of SiO2 aerogel film on copper metal substrate was revealed to induce a modification of metal surface. The modified and oxidized state of copper surface formed during the formation of the aerogel film was found to be not greatly influenced on the leakage current behavior Of SiO2 aerogel/Cu system. (C) 2003 Elsevier Science B.V. All rights reserved.