An overhead gas distribution electrode forming at least a portion of the ceiling of a plasma reactor has a bottom surface facing a processing zone of the reactor. The electrode includes a gas supply manifold for receiving process gas at a supply pressure at a top portion of the electrode and plural pressure-dropping cylindrical orifices extending axially relative to the electrode from the gas supply manifold at one end of each the orifice. A radial gas distribution manifold within the electrode extends radially across the electrode. Plural axially extending high conductance gas flow passages couple the opposite ends of respective ones of the plural pressure-dropping orifices to the radial gas distribution manifold. Plural high conductance cylindrical gas outlet holes are formed in the plasma-facing bottom surface of the electrode and extend axially to the radial gas distribution manifold.