Techniques and mechanisms to provide electrical insulation between a gate and a channel region of a non-planar circuit device. In an embodiment, the gate structure, and insulation spacers at opposite respective sides of the gate structure, each extend over a semiconductor fin structure. In a region between the insulation spacers, a first dielectric layer extends conformally over the fin, and a second dielectric layer adjoins and extends conformally over the first dielectric layer. A third dielectric layer, adjoining the second dielectric layer and the insulation spacers, extends under the gate structure. Of the first, second and third dielectric layers, the third dielectric layer is conformal to respective sidewalls of the insulation spacers. In another embodiment, the second dielectric layer is of dielectric constant which is greater than that of the first dielectric layer, and equal to or less than that of the third dielectric layer.