The invention describes MOSFETs or Metal–Oxide–Semiconductor Heterostructure Field-Effect Transistor (MOSHEMTs) with GaN 9 or other N-containing semiconductor's device containing thermally oxidized polysilicon. The SiO2 dielectric layer is achieved through thermally oxidizing the N-containing semiconductor's Polysilicon layer that rests on top of the semiconductor. The resulting layer of SiO2 is a high-quality oxide with improved properties over deposited oxides that are produced by chemical vapor deposition. The final dielectric stack is comprised of this thermal SiO2 and a thin layer of native like Ga2O3 at the interface with the AlGaN polarizing layer, which results in a very low Interface States Density (Dit) values. Controlling the temperature of thermal oxidation gives better control of the oxidation rate of the silicon dioxide layer. Since SiO2 limits the rate of oxidation of the nitride semiconductor, one can decrease the rate at which oxidizing species that reach the nitride semiconductor by increasing the thickness of the deposited silicon.