The present disclosure relates to a silicon-on-insulator (SOI) substrate structure with a buried dielectric layer for radio frequency (RF) complementary metal-oxide semiconductor (CMOS) switch fabrications. The buried dielectric layer suppresses back-gate transistors in the RF CMOS switches fabricated on the SOI substrate structure. The SOI substrate structure includes a silicon handle layer, a silicon oxide layer over the silicon handle layer, a buried dielectric layer over the silicon oxide layer, and a silicon epitaxy layer directly over the buried dielectric layer.