A showerhead electrode assembly of a plasma processing apparatus includes a thermal control plate attached to a showerhead electrode, and a top plate attached to the thermal control plate. At least one thermal bridge is provided between opposed surfaces of the thermal control plate and the top plate to allow electrical and thermal conduction between the thermal control plate and top plate. A lubricating material between the thermal bridge and the top plate minimizes galling of opposed metal surfaces due to differential thermal expansion between the top plate and thermal control plate. A heater supported by the thermal control plate cooperates with the temperature controlled top plate to maintain the showerhead electrode at a desired temperature.