This paper reviews our experimental results for electrical transport properties of nano-scale silicon metal-oxide-semiconductor field-effect transistors (MOSFETs). We used very small devices produced using 10-nm-scale lithographic techniques: electrically variable shallow junction MOSFETs (EJ-MOSFETs) and lateral hot-electron transistors (LHETs). With LHETs we succeeded in directly detecting the hot-electron current and estimated the characteristic length to be around 25 nm. We also investigated the energy relaxation mechanism by performing measurements at various applied voltages and temperatures. Furthermore, we clearly observed the tunneling current between the source and drain (source-drain tunneling) in an 8-nm-gate-length EJ-MOSFET. Based on these experimental results, we predict the limitation of MOSFET miniaturization to be around 5 nm in the source-drain tunneling scheme.