A new Pt-InAlP metal oxide semiconductor Schottky diode hydrogen sensor with highly sensitive hydrogen detection among wide operating temperature regime is demonstrated and studied. Experimentally, the studied hydrogen sensor can be operated systematically either under forward or reverse bias conditions. At 30 degrees C, the relatively hydrogen detection ratio S-r value is increased from 108.8% (107.4%) to 943.1% (1337.3%), under the forward (reverse) bias of 0.3 V, when the hydrogen concentration is increased from 4.3 to 9970 ppm H-2/air. Note that even an extremely low hydrogen concentration of 4.3 ppm H-2/air can be effectively detected at the temperature of 30-250 degrees C. (c) 2006 The Electrochemical Society.