In this paper, a comprehensive charge-based predictive model of interface and oxide trapped charges in undoped symmetric long-channel double-gate MOSFETs is developed. The model involves essentially no fitting parameters, but first-principle calculations of both oxide and Si/oxide interface trapping. This charge-based approach represents an essential step toward compact modeling of ionizing dose and aging effects in advanced field effect devices. The soundness of this approach is confirmed by extensive comparisons with numerical TCAD simulations, while the analytical formulation helps understanding the most relevant parameters of the phenomena with respect to a specific technology. The model confirms its validity for all regions of operation, i.e., from deep depletion to strong inversion and from linear to saturation.