In this paper we have shown the modeling of Lateral Double-Diffused MOS (LDMOS) transistor. A LDMOS structure can be divided into two parts, intrinsic channel and extended drift region. The intinsic channel region is modeled by industry standard BSIM6 model and extended drift region has been modeled by the modified CMC standard model of R3. The R3 model of non-linear resistor, which includes physical effects like velocity-saturation, self-heating etc. has been modified to include gate bias dependency. The new model has been validated with technology computer-aided design (TCAD) simulations and measured data from ON Semiconductor. The model (which is the combination of BSIM6 and R3 models) shows excellent agreement with the TCAD simulations and measured data.