Apparatus for an on-chip decoupling capacitor. The capacitor includes a bottom electrode that consist of nanostructures deposited over a planarized metal, a dielectric material deposited over the nanostructures, and a top electrode deposited over the dielectric material. The shape of the bottom electrode is tunable by modulating the diameter and/or the length of the nanostructures to produce an increase in capacitance without increasing the footprint of the on-chip decoupling capacitor.