Leakage current in nano-scale MOSFET has been calculated using variety of tunnel oxides. Firstly, this paper evaluates the leakage current in MOSFET devices when using SiO2 as tunnel oxide. When the thickness of tunnel oxide decreases into 1,4 nm, the leakage current will raise and cause power dissipation about 40 percent. Leakage current can be reduced by using high-K materials as tunnel oxides. Thicker high-K materials as tunnel oxides are easier to fabricate than SiO2 tunnel oxides with the thickness down to 1,4 nm. In term of Equivalent Oxide Thickness (EOT), using high-K materials for tunnel oxides could give the better performance as 1,4nm SiO2 which is also more simple in the fabrication. Here, we also evaluates the leakage current as the function of temperature, channel length, and oxide thickness. Computational result shows that using HfO2 to replace SiO2 as tunnel oxides can make leakage current decrease up to seven times. For practically use, HfO2 were suiTable as tunnel oxide in memory devices, particularly in quantum dot (QD) floating gate memory. In this case we use heterostructure QD consisting Si/Ge/Si as electronic storage node. The results demonstrated that the memory operation using HfO2 as tunnel oxide has a better performance rather than SiO2.