High-temperature off-state characteristics of thin-SOI RESURF LDMOS transistors were studied experimentally and theoretically and compared with off-state characteristics of junction-isolated bulk-Si power devices. At 200/spl deg/C, the off-state leakage current in the SOI devices was approximately 200 times lower than in the bulk-Si devices with a comparable breakdown voltage and on-resistance. At 300/spl deg/C, well beyond the operating range of the bulk devices, the off-state leakage current in the SOI devices was only 1.5 nA/μm. The leakage current appears to scale with the thickness of the SOI layer. The results of this study indicate that LDMOS transistors fabricated in thin SOI layers are well suited for high-temperature power IC applications.