Abstract: A plasma reactor showerhead electrode assembly for processing semiconductor wafers comprised of a typically silicon disk shaped gas plate having a plurality of gas passage holes therethrough, and a graphite circular split collar assembly including first and second semicircular sections forming a circumferential inner slot when opposing ends of said sections are secured together, the slot mating in a dovetail connection with an outer circumferential groove of said gas plate for retaining the latter between said sections. A conductive gasket may be interposed between the gas plate groove and the mating collar assembly to provide an electrically and thermally conductive seal. The first and second semicircular sections have opposing ends screwed or pinned together for providing easy disassembly thereof for replacement of the gas plate.