O-2 plasma ashing is commonly used to remove photoresist. The effect of O-2 plasma ashing on the porous organosilicate glass (CH3SiO1.5)(n), one of the spin-on materials, is investigated. O2 plasma can oxidize the methyl groups in porous organosilicate glass (POSG), which leads to the formation of Si-OH groups. The hydrophilic Si-OH groups will induce moisture uptake so that electrical degradation will occur in POSG film. Pure hexamethyldisilazane (HMDS) vapor (100% HMDS) can react with the Si-OH groups in POSG film. It converts hydrophilic Si-OH groups into hydrophobic Si-O-Si(CH3)(3) groups against moisture uptake. The leakage current density decreases by a factor of 2-3 and the dielectric constant decreases from 3.62 to 2.4 when O-2 plasma-damaged POSG undergoes HMDS treatment at 80degreesC for 15 min. Therefore, HMDS treatment is the effective technique to repair the electrical degradation to POSG film during photoresist stripping processing.