Metal capacitor stacked with a MOS capacitor to provide increased capacitance density

An on-chip capacitive device comprises a semiconductor substrate, a MOS capacitor formed on the semiconductor substrate, and a metal interconnect capacitor formed at least in part in a region above the MOS capacitor. The MOS capacitor and the metal interconnect capacitor are connected in parallel to form a single capacitive device. The capacitance densities of the MOS capacitor and the metal interconnect capacitor are, thereby, combined. Advantageously, significant capacitance density gains can be achieved without additional processing steps.