Al‐Al2O3‐Pd MIM (metal insulator metal) junctions fabricated on a glass substrate were tested as hydrogen sensors. The I‐V (current versus voltage) characteristics of the junctions were measured at room temperature in a vacuum of 10-5 Torr and in H2 gas of 10-2–100 Torr. A significant increase in the current was observed upon introduction of H2 gas. This phenomenon is believed to occur due to the work function lowering of the hydrogen‐absorbed Pd top electrode. The rise time was on the order of minutes, while the recovery time when hydrogen was purged was more than 20 h. However, when the junction was placed in an oxidizing ambient such as air, the recovery time was drastically reduced to the order of minutes, indicating that the device is operative as a hydrogen sensor in the atmospheric ambient. Hydrogen adsorption and desorption behavior of the Pd film was also investigated using a Pd coated quartz microbalance, and the results explained the current response of the Pd MIM junction to hydrogen in the presence of oxygen.