A structured dielectric layer and fabrication process for separating wiring levels and wires within a level on a semiconductor chip is described incorporating a lower dielectric layer having narrow air gaps to form dielectric pillars or lines and an upper dielectric layer formed over the pillars or fine lines wherein the air gaps function to substantially reduce the effective dielectric constant of the structured layer. The invention overcomes the problem of solid dielectric layers which would have the higher dielectric constant of the solid material used.