A novel scaling theory for fully depleted pi-gate (Pi G) MOSFETs is presented. The natural length for Pi G MOSFET is obtained by solving the equation of equivalent number of gates (ENG), where the ENG of the Pi G device monitored by the control factor eta can be a linear combination of ENGs for both the triple-gate (TG) and quadruple-gate (QG) transistors. Numerical device simulation data for drain-induced barrier lowering (DIBL) were compared to the model to validate the theory. Among the Pi G devices with the same normalized gate extension depth (NGED = t(ex)/t(si)) in the buried oxide, one with the largest cross-section will show the worst immunity to DIBL effects due to the smallest ENG and largest natural length. For equivalent short-channel gate controlling capability, the Pi G MOSFET with NGED = 0.2 corresponding to the control factor of eta = 0.49 illustrates an improvement of up to 23% in the minimum effective channel length L-min when compared to the double-gate (DG) MOSFET. (C) 2014 Elsevier Ltd. All rights reserved.