We present a three-layer dielectric continuum model to study the electrical polarization properties of metal-oxide semiconductor heterostructures. The heterostructures are composed of c-plane (0001) wurtzite-structure (piezoelectric) ZnO and polycrystalline (111) textured perovskite-structure (ferroelectric) BaTiO3, which reveal coupling effects between the non-switchable ionic charge of the wurtzite-structure layer and the electrically switchable lattice charge of the perovskite structure layer at their common interfaces. This model expands our previous two-layer model approach [J. Electron. Mater 37, 1029 (2008)]. We calculate and discuss the highly symmetric Sawyer-Tower circuit response. The ferroelectric polarization in the BaTiO 3 layer gives rise to hysteresis observation. Formation of depletion zones within the ZnO layers produces polarization offsets, which strongly depend on the spontaneous polarization orientation and magnitude within the ZnO layers. Our model is in excellent qualitative agreement with experimental data from a ZnO-BTO-ZnO heterostructure, and we identify the spontaneous polarization orientation in both wurtzite structure ZnO layers by comparison with our model.