Abstract: According to the applications of modern LED driver ICs and the advantages of SOI technology for power ICs,we analyze the breakdown theory of the SOI device and propose the design project for 500V class high votage devices.An optimized SOI LDMOS device with 40μm linearly graded doping profile drift region is designed and simulated by TCAD tool,then CMOS compatible processes are developed and implemented successfully.Off-state breakdown voltage of the device can reach 550V,and the specific on-resistance is 5.8Ω·mm².