  Fluctuations are strong in mesoscopic systems and have to be taken into
account for the description of transport. We show that they can even be used as
a resource for the operation of a system as a device. We use the physics of
single-electron tunneling to propose a bipartite device working as a thermal
transistor. Charge and heat currents in a two terminal conductor can be gated
by thermal fluctuations from a third terminal to which it is capacitively
coupled. The gate system can act as a switch that injects neither charge nor
energy into the conductor hence achieving huge amplification factors.
Non-thermal properties of the tunneling electrons can be exploited to operate
the device with no energy consumption.
