Multiple threshold voltage circuitry based on silicon-on-insulator (SOI) technology is disclosed which utilizes N-wells and/or P-wells underneath the insulator in SOI FETs. The well under a FET is biased to influence the threshold voltage of the FET. A PFET and an NFET share a common buried P-well or N-well. Various types of logic can be fabricated in silicon-on-insulator (SOI) technology using multiple threshold voltage FETs. Embodiments provide circuits including the advantageous properties of both low-leakage transistors and high-speed transistors.