The nonlinear electrohydrodynamic stability of two superposed dielectric fluids is studied. The system is stressed by a normal electric field such that it allows for the presence of surface charges at the interface. The method of multiple scale perturbations is used to obtain two nonlinear Schro¨dinger equations describing the behavior of the disturbed system. The stability of the perturbed system is discussed both analytically and numerically and stability diagrams are obtained. The electric field plays a dual role in the sense that it can stabilize the system for relatively large values of wavenumbers and small values of the density ratio and vice versa. The stabilizing range of the electric field for some given density ratios is tabulated. The analogy with hydromagnetic stability is established. Expressions for the surface elevation and the cutoff wavenumber separating stable and unstable disturbances are also obtained.