A method and system for modeling silicon-on-insulator shallow trench isolation stress effect is described. The method includes creating instance parameters that define dimensions of a body-tie enclosure of gate and gate-end. The instance parameters are added to a netlist. The netlist and a lookup table are used to generate a mobility multiplier. The mobility multiplier is added to the netlist and a circuit simulation program runs the netlist having the instance parameters and the mobility multiplier.