Abstract: A radio frequency integrated circuit with a silicon-on-insulator substrate includes a buried oxide layer that is disposed over a silicon substrate. The silicon-on-insulator substrate has a silicon layer that is disposed over the buried oxide layer. The integrated circuit includes a transistor disposed on the silicon layer, and a guard-ring in the silicon-on-insulator substrate that surrounds the transistor on the silicon layer. Depletion regions on the silicon substrate corresponding to areas surrounding the transistor is defined by the application of a voltage to the guard-ring. Isolation of radio frequency transmission lines on silicon-on-insulator substrates is also possible with this configuration.