In three-dimensional integration technology, through-silicon vias (TSVs) with a high aspect ratio in excess of 10 are required, due to a strong demand for a higher packing density. We achieved perfect conformal electroless plating of Cu by the addition of Cl- and bis(3-sulfopropyl) disulfide to a standard plating bath. With this technology, the Cu thickness of the TSV sidewalls remained constant with depth, even for the TSV with an aspect ratio of 20. Perfect conformal plating is a promising technology that could lower the resistance of high aspect ratio TSVs. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3193535] All rights reserved.