Abstract: A method for generating input data for a SPICE simulator in which a preprocessor computer program automatically assigns one of the models in the SPICE deck for modeling a particular device in a circuit simulated by the SPICE deck. Data which specifies valid device size ranges for a particular model is added to the SPICE deck prior to preprocessing. The model is assigned by the preprocessor computer program based upon device size, whether it is connected to power supply or ground and device type (P or N). The preprocessor output data is in a format usable by a commercially available SPICE program.