A continuous and analytical surface potential model for SOI LDMOS, which accounts for automatic transitions between fully and partially-depleted statuses,is presented. The surface potential equation of the SOI de- vice is solved by using the PSP′s accurate algorithm of surface potential,and the front and back surface potentials are obtained analytically as a function of gate and drain voltage. The formulations of inversion charge and body charge under the fully-depleted state have been modified. The continuous and analytical DC model for SOl LD- MOS is given based on PSP. The comparisons between simulation and measurements indicate that this model can predict the DC characteristics of SOI LDMOS accurately.