  We show in this article that phase change materials (PCM) exhibiting a phase
transition between a dielectric state and a metallic state are good candidates
to perform modulation as well as amplification of radiative thermal flux. We
propose a simple situation in plane parallel geometry where a so-called
radiative thermal transistor could be achieved. In this configuration, we put a
PCM between two blackbodies at different temperatures. We show that the
transistor effect can be achieved easily when this material has its critical
temperature between the two blackbody temperatures. We also see, that the more
the material is reflective in the metallic state, the more switching effect is
realized whereas the more PCM transition is stiff in temperature, the more
thermal amplification is high. We finally take the example of VO2 that exhibits
an insulator-metallic transition at 68{\textdegree}C. We show that a
demonstrator of a radiative transistor could easily be achieved in view of the
heat flux levels predicted. Far-field thermal radiation experiments are
proposed to back the results presented.
