A method of fabricating a gate of a transistor device on a semiconductor substrate, includes the steps of placing the substrate in a vacuum chamber of a plasma reactor and introducing into the chamber a process gas that includes oxygen while maintaining a vacuum pressure in the chamber. An oxide insulating layer on the order of several Angstroms in thickness is formed at the surface of the substrate by generating a plasma in a plasma generation region within the vacuum chamber during successive "on" times, and allowing ion energy of the plasma to decay during successive "off" intervals separating the successive "on" intervals, the "on" and "off" intervals defining a controllable duty cycle. During formation of the oxide insulating layer, the duty cycle is limited so as to limit formation of ion bombardment-induced defects in the insulating layer, while the vacuum pressure is limited so as to limit formation of contamination-induced defects in the insulating layer. A conductive gate electrode is formed over the insulating layer.