Showerhead electrode assemblies are disclosed, which include a showerhead electrode adapted to be mounted in an interior of a vacuum chamber; an optional backing plate attached to the showerhead electrode; a thermal control plate attached to the backing plate or to the showerhead electrode at multiple contact points across the backing plate; and at least one thermally and electrically conductive gasket separating the backing plate and the thermal control plate, or the backing plate and showerhead electrode, at the contact points. Methods of processing semiconductor substrates using the showerhead electrode assemblies are also disclosed.