A new analytical model of high voltage silicon on insulator(SOI) thin film devices is proposed,and a formula of silicon critical electric field is derived as a function of silicon film thickness by solving a 2D Poisson equation from an effective ionization rate,with a threshold energy taken into account for electron multiplying.Unlike a conventional silicon critical electric field that is constant and independent of silicon film thickness,the proposed silicon critical electric field increases sharply with silicon film thickness decreasing especially in the case of thin films,and can come to 141 V/μm at a film thickness of 0.1 μm which is much larger than the normal value of about 30 V/μm.From the proposed formula of silicon critical electric field,the expressions of dielectric layer electric field and vertical breakdown voltage(VB,V) are obtained.Based on the model,an ultra thin film can be used to enhance dielectric layer electric field and so increase vertical breakdown voltage for SOI devices because of its high silicon critical electric field,and with a dielectric layer thickness of 2 μm the vertical breakdown voltages reach 852 and 300V for the silicon film thicknesses of 0.1 and 5 μm,respectively.In addition,a relation between dielectric layer thickness and silicon film thickness is obtained,indicating a minimum vertical breakdown voltage that should be avoided when an SOI device is designed.2D simulated results and some experimental results are in good agreement with analytical results. A new analytical model of high voltage silicon on insulator (SOI) thin film devices is proposed, and a formula of silicon critical electric field is derived as a function of silicon film thickness by solving a 2D Poisson equation from an effective ionization rate, with a threshold energy taken into account for electron multiplying. Unlike a conventional silicon critical electric field that is constant and independent of silicon film thickness, the proposed silicon critical electric field increases sharply with silicon film thickness especially especially in the case of thin films, and can come to 141 V / μm at a film thickness of 0.1 μm which is much larger than the normal value of about 30 V / μm. From the proposed formula of silicon critical electric field, the expressions of dielectric layer electric field and vertical breakdown voltage (VB , V) are obtained. Based on the model, an ultra thin film can be used to enhance dielectric layer electric field and so increase vertical breakdown voltage fo r SOI devices because of its high silicon critical electric field, and with a dielectric layer thickness of 2 μm the vertical breakdown voltages reach 852 and 300V for the silicon film thicknesses of 0.1 and 5 μm, respectively. thickness and silicon film thickness is obtained, indicating a minimum vertical breakdown voltage that should be be taken when an SOI device is designed.2D simulated results and some experimental results are in good agreement with analytical results.