Abstract : We present low temperature electronic transport measurements in silicon-on-insulator nano-MOSFETs. Their electrical properties depend in particular on the junctions between the reservoirs and the transistor channel, determined during fabrication by the spacers deposited on both sides of the gate. The behaviour differences are emphasized at low temperature. In ultra-scaled transistors, with a typical gate length of 30 nm, dopants diffusion during activation annealing can result in a single dopant well coupled to the reservoirs located in the middle of the channel, below the gate. It is revealed at low temperature below the transistor threshold by resonant tunnelling through its energy levels. An estimation of its ionization energy gives an enhanced value as compared to the bulk value, attributed to the dielectric confinement of the donor. On the contrary, electrons can be confined in the transistor channel by high enough access resistances. Thus samples turn at low temperature into single electron transistors, with the island located below the gate. It is extended to coupled dots systems, by depositing several gates between source and drain. Their behaviour depends on the distance between gates and on spacers length. These systems are used to transfer a single electron.