Proton bombardment technology is integrated into the standard IC process as a post-backend process module to form local semi-insulating regions on mixed-signal/RF chips. With 10/sup 15/ cm/sup -2/, 100 /spl mu/m deep bombardment through mask windows, /spl rho//sub s/=20k/spl sim/50k /spl Omega/.cm regions are formed, which are thermally stable at 200/spl deg/C. High-Q inductors and reliable MOSFETs are made on same chip with no need of tuning the existing wafer process. Design rules are established.