Abstract: Patterned SOI substrates were fabricated by masked SIMOX technology, and patterned SOI LDMOSFETs were fabricated by using a simple process compatible to conventional SOI CMOS technology. The devices shows good electrical performance, including flat output characteristic curves, an on-state breakdown voltage of 6V, an off-state breakdown voltage of 13V, a leakage current of 10^-8A, a cut-off frequency of 8GHz, and a small signal voltage gain of 6dB at 1 GHz and the drain supply voltage of 3.6V. This patterned SOI LDMOS is a promising RF power device.