We report results of studying some natural properties of highly disordered mesoscopic systems which seem to be promising for elevating quantum device work temperatures up to 77-300 K. They are FET-type Si-MNOS (metal-nitride-oxide-semiconductor) structures with built-in charge concentrations being so high that the systems remain to be strongly disordered even at room temperature. Disorder of studied structures could be controlled by varying charged traps concentration at the SiO2-Si3N4 interface that induce strong potential fluctuations. Important feature of the structures is the possibility to vary the built-in charge over a wide range (up to 1013 CM−2) that results in varying the disorder range. The conductance of such a system is shown to be controlled by the single small quantum-sized region with a ballistic transport which is a saddle-point region of the fluctuation relief. Narrowness of that “bottle neck” (comparable with the electron wavelength) results in quantizing conductance of the structure, and if the disorder is high enough, the conductance for some gate voltages shows a real tendency to reach a plateau at the quantum value e2/h. What is important, that tendency occurs a∼t high temperatures (77-300 K).