PURPOSE: To obtain a parameter extraction system capable of automatically fitting a parameter to be optimized, making it unnecessary for a user to specify a parameter and reducing user's intelligent load.

CONSTITUTION: This system is provided with memories (a ROM 3 and a RAM 4), a processor 1, an I/O circuit 2, a bus 5 for connecting respective units, a display means EWS 7, an external data storing means 8, etc., and the processor 1 applies parameter fitting based upon least square to measuring data loaded into the RAM 4 by using a program built in the ROM 3. As the preprocessing of fitting based upon the method of least squares, the processor 1 executes sensitivity analysis in each shape of a transistor and each electric characteristic (drain and gate characteristics) and dynamically determines the combination of parameters to be optimized.