This paper introduces a semi-empirical dynamic model for PEM fuel cell power modules with potential applications in distributed generation. The proposed model is constructed based on the measurements from a Nexa™ PEM fuel cell power module under different load conditions, and the model has been validated by static as well as dynamic tests. The effects of temperature and variations in the internal impedance under different load conditions have been studied. The results have indicated that the model provides an accurate representation of the dynamic and static behaviors of the fuel cell power module.