In this work, the preliminary study and a design method for the VLW (Variation of Lateral Width) SOI LDMOS device have been proposed. A capacitance-based analytical model and the adjusted critical electric model have been presented for this special structure. The relationship between the optimized drift doping concentration and the breakdown voltage with the other parameters of the VLW structure have been presented in detail. (C) 2015 Elsevier Ltd. All rights reserved.