A substrate voltage generator is disclosed which provides over 1.5 times as much current for a given size circuit, as has been capable with prior art substrate voltage generators. This is achieved by means of a high capacitance per unit area charge pumping capacitor having a triple plate structure and further through the space saving technique of providing a dual use for the source diffusion of the current sinking device in the circuit so as to also serve as the guard ring around the charge pumping circuit of the substrate voltage generator. These and other features of the substrate voltage generator circuit enable relatively large quantities of current to be supplied for maintaining the substrate voltage in large dimension VLSI chips having significant diffusion leakage currents.