By solving 2-D Poisson’s equation, a new analytical model to calculate the electric field distribution of a SOI RESURF device with Dual Conduction Layers (Dual-CL) is firstly proposed. The proposed model is also available for the single RESURF and triple RESURF SOI devices without any modification. A matrix equation is developed for the determination of the lateral and vertical breakdown voltages, in which the influences of the N-top layer, P-top layer, and the N-drift region are all considered. A unified RESURF criterion of single RESURF, triple RESURF, and Dual-CL SOI devices is further derived for optimizing the structure parameters. A good agreement between the analytical results and the numerical results shows that the N-top layer and P-top layer have opposite impacts on the breakdown performance of Dual-CL SOI devices. In addition, an optimal trade-off between the breakdown voltage and the specific on-resistance for the triple RESURF and Dual-CL SOI devices is obtained due to the incorporation of the P-top layer.