  This paper discusses how classical transport theories such as the thermionic
emission, can be used as a powerful tool for the study and the understanding of
the most complex mechanisms of transport in Fin Field Effect Transistors
(FinFETs). By means of simple current and differential conductance
measurements, taken at different temperatures and different gate voltages
($V_G$'s), it is possible to extrapolate the evolution of important parameters
such as the spatial region of transport and the height of thermionic barrier at
the centre of the channel. Furthermore, if the measurements are used in
conjunction with simulated data, it becomes possible to also extract the
interface trap density of these objects. These are important results, also
because these parameters are extracted directly on state-of-the-art devices and
not in specially-designed test structures. The possible characterisation of the
different regimes of transport that can arise in these ultra-scaled devices
having a doped or an undoped channel are also discussed. Examples of these
regimes are, full body inversion and weak body inversion. Specific cases
demonstrating the strength of the thermionic tool are discussed in sections
\ref{sec:II}, \ref{sec:III} and \ref{sec:IV}. This text has been designed as a
comprehensive overview of 4 related publications (see Ref. [2-5]) and has been
submitted as a book chapter in Ref. [6]).
