A simulation parameter extracting method of a MOS transistor according to an exemplary aspect of the present invention includes evaluating a measured value that includes a true gate-overlap capacitance by measuring a capacitance between the gate and the drain in each of a plurality of layout patterns at a predetermined bias voltage, only the number of contact plugs being different for each layout pattern, evaluating a gate-overlap capacitance calculation value of each layout pattern by subtracting a contact parasitic capacitance between the contact plug and the gate from the measured value, the contact parasitic capacitance being obtained by a simulation with varying a model parameter for evaluating a parasitic capacitance between the contact plug and the gate, and extracting the gate-overlap capacitance calculation value as the true gate-overlap capacitance at the model parameter when the gate-overlap capacitance calculation value is about constant regardless of the number of the contact plugs.