The present invention relates generally to plasma processing and, more particularly, to plasma processing chambers and electrode assemblies used therein. According to one embodiment of the present invention, an electrode assembly is provided comprising a thermal control plate, a silicon-based showerhead electrode, a thermally conductive gasket, and a plurality of o-rings, wherein respective profiles of a frontside of the thermal control plate and a backside of the showerhead electrode cooperate to define a thermal interface. The thermally conductive gasket and the o-rings are positioned along this thermal interface with the o-rings separating the thermally conductive gasket from the showerhead passages such that the gasket is isolated from the showerhead passages. The gasket may facilitate heat transfer across the thermal interface from the showerhead electrode to the thermal control plate.