A method of calculating the theoretical capacitance-voltage characteristics of heavily doped silicon/insulator/silicon capacitors is presented. Unlike previously published models the capacitance-voltage characteristics are derived using Fermi-Dirac statistics and energy bandgap reduction to account for the degenerate doping levels. The method of computing the ideal characteristics for the case of degenerate doping is outlined, and the capacitance-voltage behaviour is compared with the results obtained using a Maxwell-Boltzmann distribution. The two solutions are compared as a function of doping concentration and insulator thickness to determine the errors which result when Maxwell-Boltzmann statistics are assumed. The significance of these simulations to integrated capacitors in analogue MOS circuits is discussed. Furthermore, the simulations obtained from the complete Fermi-Dirac solution are compared with measured capacitance-voltage characteristics of heavily doped n-type polysilicon/oxide/polysilicon capacitors from two different 1 mum analogue CMOS processes. It is demonstrated how the simulations can be used to estimate the electrically active doping concentration at the two oxide/polysilicon interfaces. The influence of fixed oxide charge on the capacitance-voltage behaviour is also examined.