Developing high performance hydrogen (H_{2}) sensors is of utmost importance to facilitate the safe usage of H_{2} as the alternative source of clean and renewable energy. We present an ultra-sensitive H_{2} sensor operating in air and based on electrostatically formed nanowire (EFN) sensor decorated by palladium nanoparticles (Pd NPs). By appropriate tuning of the various gate voltages of the EFN, an extremely high sensor response of ∼2 × 10^{6} % (0.8 % H_{2} exposure) and a sensitivity of ∼400 % ppm^{−1} is obtained at room temperature (20 ± 2 °C). This sensor outperforms, to the best of our knowledge, most of the reported resistive and field effect transistor (FET) based H^{2} sensors. The EFN power consumption varies from few pW to ∼436 nW at maximum current operation thus enabling ultra-low power usage at room temperature. In addition, the sensor exhibits fast response and recovery times, retains good sensing performances even at 50 % relative humidity (RH) and exhibits reproducibility over time. Combining Pd NPs with the unique features of the EFN platform makes Pd-EFN a versatile, robust, low power, rapid, and highly sensitive H_{2} sensor
