A novel large-signal equivalent circuit model of RF-SOI LDMOS based on Philips MOS Model 20 （MM20） is presented. The weak avalanche effect and the power dissipation caused by self-heating are described. The RF parasitic elements are extracted directly from measured S-parameters with analytical methods. Their final values can be obtained quickly and accurately through the necessary optimization. The model is validated in DC,AC small-signal,and large-signal analyses for an RF-SOI LDMOS of 20-fingers （channel mask length, L = 1μm,finger width, W = 50μm） gate with high resistivity substrate and body-contact. Excellent agreement is achieved between simulated and measured results for DC, S- parameters （10MHz-0.01GHz）, and power characteristics, which shows our model is accurate and reliable. MM20 is improved for RF-SOI LDMOS large-signal applications. This model has been implemented in Verilog-A using the ADS circuit simulator （hpeesofsim）.
