Disclosed herein are IC structures with decoupling capacitors based on dummy TSV plates provided in a support structure (e.g., a substrate, a die, a wafer, or a chip). An example decoupling capacitor includes first and second capacitor plates and a capacitor insulator between them. Each capacitor plate is a different blind, plate-like opening in the support structure, the openings at least partially filled with one or more conductive materials. The capacitor plate openings are referred to herein as “dummy TSV plates” because they may be fabricated while providing regular TSV openings in the support structure. Such decoupling capacitors may be better suited for high-speed microprocessor applications than conventional off-chip decoupling capacitors and may advantageously allow integrating on-chip decoupling capacitors with an ample amount of capacitive decoupling, limited or no additional processing steps on top of regular TSV processing, and in areas that may not have been used otherwise.