  Today the availability of high mobility graphene up to room temperature makes
ballistic transport in nanodevices achievable. In particular, p-n-p transistor
in the ballistic regime gives access to the Klein tunneling physics and allows
the realization of devices exploiting the optics-like behavior of Dirac
Fermions (DF) as in the Vesalego lens or the Fabry P\'erot cavity. Here we
propose a Klein tunneling transistor based on geometrical optics of DF. We
consider the case of a prismatic active region delimited by a triangular gate,
where total internal reflection may occur, which leads to the tunable
suppression of the transistor transmission. We calculate the transmission and
the current by means of scattering theory and the finite bias properties using
Non Equilibrium Green's Function(NEGF) simulation.
