The method of extracting MOSFET model parameters using optimization offers significant advantages over classical methods of extracting model parameters sequentially. Previous work in this field has concentrated on speed of convergence rather than general applicability. Gradient following methods have been applied to this problem but difficulties arise because of parameter redundancy, singularities in the objective function, and the necessity of providing very good initial estimates of the model parameters. These factors can seriously hinder the application of the technique. This paper describes the application of the simplex direct search optimization method to this problem. This algorithm, in wide use for general optimization problems, needs no derivative calculation and has proved highly stable for MOS model parameter extraction. Its basis is described and an example of its use given.