In this paper, a method to extend the detection range of hydrogen sulfide (H₂S) gas sensor is demonstrated. The sensor is based on AlGaN/GaN high electron mobility transistors (HEMTs) with Pt gate. It is observed that the as-fabricated devices exhibited sensing signal saturation at 30 ppm H₂S exposure in dry air. A pre-treatment using H₂ pulses in dry air ambient at 250 °C was applied to extend the detection range of the sensor. The H₂ treated H₂S gas sensor was able to detect a higher H₂S concentration up to 90 ppm at 250 °C without complete saturation.