Abstract: The invention relates to a method of manufacturing field effect transistors of gallium arsenide obtained by ion implantation of light donors, such as silicon or selenium, in a semi-insulating substrate of gallium arsenide. In order to reduce out-diffusion of the deep level (EL.sub.2) responsible for parasitic phenomena in the operation of the transistors, the method is characterized in that in addition oxygen ions are implanted in at least the region of the substrate intended to form the channel region of the field effect transistor. After implantation, the substrate is sintered at a temperature between 600.degree. and 900.degree. C. in either an enveloping substance or uncovered, and/or in an atmosphere of arsine.

Abstract: The invention relates to a method of treating a substrate of gallium arsenide by a double ion implantation. A first implantation of silicon ions (Si.sup.+) is carried out on the entire surface of the substrate, and a second implantation of oxygen ions (O.sup.+) is carried out in regions intended to become isolated regions. A thermal annealing treatment, preferably under encapsulation, follows these ion implantations. These implantations are carried out in order to obtain at the surface of the substrate regions of n-conductivity type isolating regions separated from each other for subsequent manufacture of semiconductor devices. The invention also relates to a gallium arsenide substrate thus treated and to a semiconductor device obtained by the technique of two ion implantations.