Although the thermochemical model attributes field-induced dielectric breakdown to time-dependent chemical bond breakage, there has been little evidence of this reported thus far. This study provides, for the first time, evidence of field-induced chemical bond disturbance using in situ Fourier transform infrared spectroscopy (FTIRS). By using porous methylsilsesquioxane as test vehicle and subjecting the film to externally applied electric field, changes in peak area ratio and intensities in the deconvoluted spectra were observed. The precursors of dielectric degradation are the Si-O and Si-OH bonds. This is a powerful technique which provides new insights into the dielectric degradation and breakdown phenomena. (C) 2004 The Electrochemical Society.