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A novel hydrogen gas sensor based on platinum titanium-oxygen (Pt-Ti-O) gate silicon-metal-insulator semiconductor field-effect transistors (Si-MISFETs) was developed. The sensor has a unique gate structure composed of titanium and oxygen accumulated around platinum grains on top of a novel mixed layer of nanocrystalline TiOx and super heavily oxygen-doped amorphous titanium formed on SiO2/Si substrates. The FET hydrogen sensors show long life times more than ten years as intrinsic chip life time by accelerated temperature aging test, and high sensing amplitude (ΔVg), which is well fitted by a linear function of the logarithm of air-diluted hydrogen concentration C(ppm), i.e., ΔVg(V)=0.355Log C(ppm)-0.610, between 100 ppm and 1%. The gradient of 0.355V/decade at 115°C is about ten times higher than that of Pt gate Si-MOSFETs hydrogen sensors. The threshold Voltage (Vth) of FETs is reproducible, and shows excellent uniformity over the 5-inch wafers, 3σVth of 178 mV.