In this study, the significant reduction of etch pits on electropolished copper surfaces was demonstrated using polyethylene glycol (PEG) and sulfuric acid as oxygen suppressors in 85 wt% phosphoric acid (H3PO4). PEG adsorbed on the copper surfaces (increasing charge-transfer resistance) and sulfuric acid increased solution acidity (enhancing viscous layer resistance) which resulted in polishing electrolytes with characteristics of decline in the reaction current but enhancement in the overpotential of oxygen formation, finally eliminating those defects. (C) 2004 The Electrochemical Society.