Characterization of the capacitance-voltage characteristics of ultrathin gate dielectrics is discussed. Focus is given to the limitations of two-element models in extracting gate capacitance from measurements of complex impedance. Of particular interest for discussion is the apparent frequency dispersion and bias dependence of accumulation capacitance. Comparison is made to a three-element model that takes into account both gate dielectric conductance and substrate resistance, but requires a measurement of complex impedance at multiple frequencies. The electrical properties of a specific alternative gate dielectric structure, namely a 10 nm Y2O3 film on silicon, are analyzed within the context of the three models. (C) 2003 Elsevier Science Ltd. All rights reserved.