Isolated complementary metal-oxide semiconductor (CMOS) devices for radio-frequency (RF) circuits are disclosed. In some aspects, an RF circuit includes CMOS devices, a silicon substrate having doped regions that define the CMOS devices, and a trench through the silicon substrate. The trench through the silicon substrate forms a continuous channel around the doped regions of one of the CMOS devices to electrically isolate the CMOS device from other CMOS devices embodied on the silicon substrate. By so doing, performance characteristics of the CMOS device, such as linearity and signal isolation, may be improved over those of conventional CMOS devices (e.g., bulk CMOS).