The effect of bias voltage polarity on the hydrogen sensing characteristics of AlGaN/GaN heterostructure Schottky diodes is reported. Under forward bias, there was a maximum observed in the sensitivity for hydrogen detection. For reverse bias, the hydrogen detection sensitivity increased proportionally to the bias voltage. A detection limit of 10 ppm of H-2 in N-2 was achieved under reverse bias with a current increase of 14% as compared to a detection limit of 100 ppm of H-2 for a similar current change under forward bias. (C) 2008 Elsevier B. V. All rights reserved.