A plasma processing apparatus is disclosed for minimizing the non-uniformity of potential distribution around wafer circumference. The apparatus includes a focus ring formed of a dielectric, and a conductor or a semiconductor having RF applied thereto. A surface voltage of the focus ring is determined to be not less than a minimum voltage for preventing reaction products caused by wafer processing from depositing thereon. The surface height, surface voltage, material, and structure of the focus ring are optimized so that the height of an ion sheath formed on the focus ring surface is either equal or has a height difference within an appropriate tolerance range to the height of the ion sheath formed on the wafer surface.