Significant improvement in the electrical isolation of closely spaced GaAs integrated circuit (IC) devices has been achieved with proton implantation. Isolation voltages have been increased by a factor of four in comparison to a selective implant process. In addition, the tendency of negatively biased ohmic contacts to reduce the current flow in neighboring MESFET's (backgating) has been reduced by at least a factor of three. The GaAs IC compatible process includes implantation of protons through the SiO2field oxide and a three-layered dielectric-Au mask which is definable to 3-µm linewidths and is easily removed. High temperature storage tests have demonstrated that proton isolation, with lifetimes on the order of 106h at 290°C, is not a lifetime limiting component in a GaAs IC process.