Very high mobility of 149∼189 cm2/Vs, large on-to-off current ratio (ION/IOff) of >7 orders of magnitude, fast turn-on sub-threshold swing of 110 mV/decade, and low power operation at 2∼2.5 V were achieved in SnO2 TFT device at an ultra-thin SnO2 thickness of 4.5 nm. The device mobility of SnO2 TFT is higher than the best ZnO-based TFTs and CVD-grown multi-layers MoS2 MOSFETs. The reached mobility is already 0.7 times of universal mobility of SiO2/Si nMOSFET, operated typically at >1 MV/cm field. The very high mobility, simple low temperature process, and ultra-thin body SnO2 transistor should find its crucial role for high resolution display, future sub-10 nm nMOSFET and brain-mimicking 3D IC.