Floating and non-floating on-chip capacitors are formed by vertical walls and/or large aspect ratio deep trenches disposed in semiconductor material. By optimizing the through spacing and substrate voltage, a very small parasitic to intended capacitance ratio may be obtained. Capacitors so formed may be used as on-chip charge storage and other types of on-chip capacitors, and eliminate or reduce the number of off-chip capacitors that would otherwise be required. The deep trench capacitors find particularly efficacious application in implantable medical devices where volume, cost and electrical energy consumption must be minimized, and preferably have capacitances which range between about 10 nF and about 1000 uF.