A novel concurrent implementation of a global-optimisation algorithm is used to extract parameter values for MESFET equivalent-circuit models. The problem of the location of the global minimum of an error function is addressed by the use of an efficient stochastic global-optimisation program which does not require accurate parameter estimates and which operates on a multiprocessor array. The program has been used to estimate the parameter values of a process-based physical equivalent model of a MESFET under multibias small-signal operation. These results are compared with those derived from an electrical equivalent-circuit model.