In this paper, theoretical analysis and experimental quantification of the gas leakage issue due to feedthroughs in anodic bonding are presented. The theoretical analysis was conducted to quantitatively analyze the influence of metal feedthroughs in anodic bonding on the package quality based on the plate elastic deformation theory and the theory of gas flow in capillaries. To validate the analysis, absolute capacitive pressure sensors were fabricated with gold feedthroughs in the silicon–glass bonding interface. The dimensions of the leakage microchannels due to feedthroughs were quantified experimentally and the leakage rate following the anodic bonding was measured using a helium leak detector. The deviations from calculated values were less than 30% in different channel dimensions and 38.3% in leakage rates between theoretical analysis and experimental studies. To address this issue, a new structure was designed, fabricated and characterized where localized Si–Au eutectic bonding was used to improve the package quality. By fine tuning two key parameters of bonding temperature and feedthrough step height, the new design was demonstrated to improve the hermetic levels by at least two orders of magnitude compared to the conventional design without eutectic bonding.