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The aim of this work is to propose a one-dimensional bipolar model of charge generation and extraction in a low density polyethylene (LDPE) under DC voltage including the effect of interfacial states. These surface states are described as an exponential distribution of traps over a 1μm depth region next to the electrodes. The distribution has a finite maximum depth, being decreasing when moving away from the electrode. In the bulk of the dielectric, we supposed that the maximum trap depth and the number of energy levels are shallower than in the interface region. Carriers are injected into the interface region via an ohmic contact by a constant source of charges on the electrode being dependent on the filling level of the exponential distribution of traps. Carriers can move from site to site in the interface region and in the bulk by getting over a potential barrier with a hopping type mobility. We present here simulation results for a unipolar model of charge transport with an interface region at each electrode. We discuss the simulated results regarding charge injection and extraction.