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Taking into account the finite lenght of the gate of a JG FET and the variation of the mobility versus electric field, it is shown, through a self-consistent hypothesis, that the electrical and geometrical properties of the active conducting channel remain unchanged in the saturation range. Experimental results of noise measurements performed in the saturation range at 300 K and 77 K can easily be explained by this theory.

Noise measurements at 77 K performed on JG FET 2 N 4416 (Texas Instruments Corporation) show an important disagreement with theoretical expressions given by Van der Ziel. By analogy with results obtained with p-type germanium samples in the presence of a moderately high electric field, the “warm-carrier” hypothesis is made for the FET channel. Experimental results in the range 77 K–300 K fit the theoretical laws deduced from this assertion.

Transverse ( T n⊥ ) and longitudinal ( T n| ) diffusion-noise temperatures are compared in isotropic semiconductors in the presence of an applied electric field E . It is shown that T n| > T n⊥ and that the ratio T n| / T n⊥ tends towards infinity at intense electric fields. Differential mobility is mainly responsible for the strong anisotropy induced by an electric field in the noise temperature. The study of such phenomena in anisotropic semiconductors requires a knowledge of the variation of the mobility tensor with the vector E .

Properties of the mobility tensor and differential mobility-tensor components in the hot-carrier range are investigated in cubic semiconductors as regards to symmetry and independently from any scattering mechanism. It is shown that all the components can be deduced from only one diagonal and one nondiagonal component. General relations between components are established. Considering conduction of each valley brings additional information which is explicated for semiconductors with valleys lying along the