<p>A HEMT type device which has pillars with vertical walls perpendicular to a substrate. The pillars are of an insulating semiconductor material such as GaN. Disposed on the side surfaces of the pillars is a barrier layer of a semiconductor material such as AlGaN having a bandgap greater than that of the insulating material of the pillars. Electron flow is confined to a narrow channel at the interface of the two materials. Suitable source, drain and gate contacts are included for HEMT operation.</p>
