M.O.S. transistor as a 4-terminal device

Taking account of the bulk charge and a finite substrate-source e.m.f., expressions are derived for the substrate and gate transconductances of a metal-oxide-semiconductor (m.o.s.) transistor. Comparison with experimental results indicates some discrepancies, but these appear to be no greater than would be expected of a first-order theory. A brief discussion of the factors affecting the substrate transconductance is given.