A method for selecting transistor design parameters. A first set of simulations is used to calculate leakage current at a plurality of sets of design parameter values, and the results are fitted with a first response surface methodology model. The first model is used to generate a function that returns a value of a selected design parameter, for which a leakage current specification is just met. A second set of simulations is used to calculate effective drive current for a plurality of sets of design parameter values, and the results are fitted with a second response surface methodology model. The second model is used, together with the first, to search for a set of design parameter values at which a worst-case effective drive current is greatest, subject to the constraint of meeting the worst-case leakage current specification.