A Pd/TiO2/Si MOS sensor (Pdtisin sensor) is proposed for the detection of hydrogen gas. The sensor is fabricated on a p-type < 111 > silicon wafer having resistivity of 3-6 Omega cm. The thickness of TiO2 in this structure is about 600 nm. The capacitance-voltage (C-V) and conductance-voltage (G-V) characteristics of the device is observed on the exposure of hydrogen gas at room temperature. The mechanism of hydrogen sensing of titanium dioxide-based MOS sensor (MOS capacitor) has been investigated by evaluating the change in flat-band voltage (V-FB) and fixed surface state density of the device in presence of hydrogen gas. The device exhibits very large parallel shift in C-V as well in G-V characteristics. The possible mechanism on Pd/TiO2 and TiO2/Si surface in presence of hydrogen gas has been proposed. The response and recovery time of the device is also measured at room temperature. (C) 2007 Elsevier Ltd. All rights reserved.