A method for fabricating a radio-frequency device involves providing a substrate structure including a silicon handle wafer, an oxide layer formed on the silicon handle wafer, and an active silicon layer disposed on the oxide layer. The method further involves patterning and etching the active silicon layer and the oxide layer to form a frontside opening in the active silicon layer and the oxide layer exposing a top surface of the silicon handle wafer and converting the exposed top surface of the silicon handle wafer to porous silicon