In this work, we report an ultra-high sensitive (S = 1.4 * 10^8 %}), prompt response and recovering Pt/Pt+SiO2 cermet layer/GaN-based hydrogen (H2) sensor. A sensor fabricated with a 15 nm cermet layer comprising of Pt and SiO2 deposited in between 15 nm Pt and GaN layers exhibits significantly enhanced sensitivity towards detection of 4 % H2 by 300 times when compared to reference Pt/GaN sensor at ambient temperature (300 K). Further, the sensitivity of the present sensor shows very weak dependence on the temperature (T) with maximum sensitivity (Smax) reducing from 1.4 * 10^8 % to 2.3 * 10^7 % as temperature increases from 300 to 423 K. The shift in threshold voltage of the test sensor (DeltaVt,test = 767 mV) increased by 50 % when compared to the shift in threshold voltage of control sensor (DeltaVt,control = 511 mV) at 1 mA/cm^2. Furthermore, the cermet sensor also demonstrates fast response (recovery) time which reduces from 4.58 (2.36) seconds to 94 (39) milliseconds as temperature increases from 300 to 423 K. The maximum sensitivity (Smax), response (tau_a) and recovery (tau_b) times of test sensor when exposed to 10000 ppm of H2 are 3.9 * 10^7 %, 30 secs and 30.1 secs respectively. The shift in threshold voltage of test sensor at 1 mA/cm^2 when exposed to 100 ppm, 1000 ppm, 5000 ppm, and 10000 ppm are 40 mV, 70 mV, 460 mV, and 600 mV respectively. The 2-Dimensional (2D) trapping of H-atoms by the oxygen atoms present in Pt+SiO_2 cermet layer and porous/compact layer models explain the underlying mechanism, which resulted in significant improvement of the sensing characteristics of test sensor. The Thermionic Emission (TE) model effectively models the current density (J) – voltage (V) characteristics of control and test sensor with and without hydrogen. The prompt detection of high percentages of hydrogen in life-saving and commercial fuel applications is possible with Pt+SiO2 cermet-based sensor with response and recovery times in the order of milliseconds for temperature range 363-423 K.© 2020 IOP Publishing Ltd.