Abstract Metal-oxide-semiconductor (MOS) capacitors Fabricated on mold cast polycrystalline silicon wafers exhibit a large stretch-out and distortion both in the capacitance-voltage as well as in the inversion capacitance-frequency characteristics. This is attributed to the high density of interface traps, which can respond to gate signals over a wide range of frequencies. The frequency behaviour of the inversion capacitance over the temperature range 30–200°C demonstrates the generation-recombination, and diffusion mechanisms of the minority carrier response to an AC gate signal. The dominance of one mechanism over the other can be characterised by a transition frequency. Arrhenius plots of the transition frequency reveal three activation energies: 1.09, 0.59 and 0.16 eV. The first two energies are attributed to the generation-recombination and diffusion mechanisms, whereas the third energy remains unidentified. A high transition temperature of 170°C is observed, which is in agreement with the high density of bulk generation-recombination centres present in the polycrystalline material.