Abstract: An etched SiO.sub.2 film component serving as a mask at the time of formation of source and drain electrodes in a surface layer of a GaAs substrate by means of ion implantation is side-etched before a gate electrode is formed. An SiO.sub.2 film component has a narrowed width smaller than a distance between the source and drain electrodes while the SiO.sub.2 film component supports a metal mask patterned film at its top surface. The SiO.sub.2 film component is replaced with a metal layer serving as a gate of a self-aligned Schottky gate FET. According to this method, a metal with high heat resistance need not be used as a metal material of the gate layer.

Abstract: A process for fabricating a field effect transistors having a source electrode, a drain electrode and a gate electrode, including the steps of forming first to third conjoined narrow portions of thin film on an active region of a semiconductor, the second thin film portion having a different etching rate from the first and third and implanting ions into the active region to form a high carrier concentration region by using the conjoined films as a mask. The thickness of the second film portion determines the gate electrode length and the thickness of the third film portion determines the distance between the high carrier concentration region at the source side and the gate electrode.