The present invention relates to a through silicon via (TSV). The TSV is disposed in a substrate including a via opening penetrating through a first surface and a second surface of the substrate. The TSV includes an insulation layer, a barrier layer, a buffer layer and a conductive electrode. The insulation layer is disposed on a surface of the via opening. The barrier layer is disposed on a surface of the insulation layer. The buffer layer is disposed on a surface of the barrier layer. The conductive electrode is disposed on a surface of the buffer layer and a remainder of the via opening is completely filled with the conductive electrode. A portion of the buffer layer further covers a surface of the conductive electrode at a side of the second surface and said portion is level with the second surface.