H2 gas sensors for different applications require various detection ranges, such as 1–100 ppm for exhale breath test and 0–40000 ppm for H2 energy vehicles. Coarse-tuning of the detection range could be realized by the selection of the type of H2 sensors. The fine-tuning of the detection range within one type of H2 sensor, however, is little concerned and reported. Herein, we propose to achieve the fine-tuning of the H2 gas detection range of the AlGaN/GaN HEMT devices by adjusting the Pt gate thickness. Devices with various Pt gate thicknesses of 2, 20, 60, and 100 nm were fabricated and investigated. Results show that the HEMT devices have excellent pinch-off characteristic with an on-to-off ratio of ∼four orders of magnitude. For the 100 nm thick device exposed to 500 ppm H2, ultrafast response time of 1.5 s is observed together with high response. With the decrease of gate thickness, both the response and the response time gradually increase, 1850% and 6 s for the 2 nm thick device. Moreover, both the low limit of detection (LOD) and the saturation cencentration decrease from 1.6 to 0.14 ppm and from 30,000 to 5000 ppm, respectively, with the gate thickness reduced from 100 to 2 nm, revealing that fine-tuning of the detection range could be achieved by adjusting the gate thickness. Finally, the response activation energy is also studied, 15.9, 19.7, and 42.8 kJ/mol for 2, 60, and 100 nm thick devices, respectively. Display omitted •Employment of AlGaN/GaN HEMT device as a H2 gas sensor.•Demonstration of a high performance H2 sensor with small LOD ∼0.14 ppm and ultrafast response ∼1.5 s.•Realization the fine-tuning of the detection range by simply adjusting the gate thickness.•Study the dependence of the response activation energy Ea on the gate thickness.