This paper introduces diffusive representation as a novel approach to characterize the dynamics of charge trapped in the dielectric layers of microelectromechanical systems. Diffusive representation provides a computationally efficient method to achieve an arbitrary order state-space model of the charging dynamics. This approach is particularly well suited to analyze the dynamics of the dielectric charge under nontrivial controls, as in the case of sliding mode controllers. The diffusive symbol of the experimental structure has been obtained from open-loop measurements, in which the pseudo random binary sequences are applied to the device. The obtained model exhibits good agreement with the experimental data and also allows us to model the behavior of the charge dynamics under excitation with arbitrary binary signals.