An analytic model is presented to estimate the avalanche breakdown voltage improvement for various lightly doped source-drain (LDD) structures. In this model, the voltage drop across the lightly doped drain region is assumed to be responsible for breakdown voltage improvement. The voltage drop is calculated by assuming a two-dimensional potential distribution in the rectangular section of the n- region. This section is treated as a volume obeying Gauss' law, thereby enabling the mobile and immobile charges contained in it to be related to the electric fields normal to its surface without considering the detailed distribution of the charges inside. The calculated results agree well with experimental and two-dimensional simulation data for a wide range of processing parameters. © 1985.