Abstract: In a plasma enhanced chemical vapor processing apparatus first and second sets of electrodes are electrically insulated one from the other via the intermediary of a plurality of insulator bodies. Each of the insulator bodies includes a recessed portion for extending the electrical path length over the surface of the insulator to minimize shorting of the insulators in use. The recess in the insulator body is of generally L-shaped cross section including a radially inwardly directed recessed portion intersecting with an axially directed recess portion. The axially directed portion of the recess is shielded from the plasma discharge, thereby reducing the probability of deposition of conductive material thereon which could otherwise result in shorting of the insulator member. The axial recesses extend into the insulator body from opposite ends thereof.