The use of AlGaNGaN high electron mobility transistor (HEMT) differential sensing diodes is shown to provide robust detection of 1% H2 in air at 25 °C. The active device in the differential pair is coated with 10 nm of Pt to enhance catalytic dissociation of molecular hydrogen, while the reference diode is coated with TiAu. The active diode in the pair shows an increase in forward current of several milliamperes at a bias voltage of 2.5 V when exposed to 1% H2 in air. The HEMT diodes show a response approximately twice that of GaN Schottky diodes, due to the presence of piezoelectric and spontaneous polarization in the heterostructure. The use of the differential pair removes false alarms due to ambient temperature variations.