Several models have been proposed in the literature to predict the performance of proton exchange membrane fuel cells (PEMFC). These models have different levels of complexity and can be divided basically into two groups: (i) mechanistic (theoretical); and (ii) semi-empirical models. The mechanistic models are obtained from electrochemical, thermodynamic, and fluid dynamic equations, and describes, with a high level of details, the processes in the operation of the fuel cell. The main drawback of the mechanistic approach is that, in general, the models are very complex, requiring the knowledge of parameters that are difficult to be obtained. Semi-empirical models, on the other hand, are easier to be obtained and can also be used to accurately predict the fuel cell system performance for engineering applications. In this paper, a new semi-empirical model, that is simpler than others presented in the literature, is proposed. It is derived by using semi-empirical equations and the resulting empirical coefficients are calculated through linear least squares. The model can be used in the evaluation of performance of small-distributed electrical generation systems, and also for the design of fuel cell systems for vehicles and portable electronics. (C) 2009 Elsevier Ltd. All rights reserved.