Abstract: In this paper, an analytical model of the surface lateral electric field for LDD MOSFET is presented. This model contains geometric and doping parameters of LDD MOSFET. It can be used to calculate the surface lateral electric field of LDD MOSFET which has lightly doped drain regions of different lengths, junction depths and doping concentrations, Using this model, the electric field of the conventional and graded drain MOSFET can also be calculated. The result obtained from this model is identical with the numerical result of FD-MINIMOS. This model can also be applied to calculate the substrate current and breakdown voltage. According to this model, the optimal geometric and doping parameters can be easily determined. The present model provides a fast method for extracting the related parameters and is a convenient tool for the LDD MOSFET design.