Changes in current by Cl2gas adsorption were measured at 200 °C for SnO2films sputtered on SiO2/Si substrates, with a varying electric field from the substrate. Properties of Cl2adsorption, such as sensitivity and reaction rate constant, under a positive (+5 V) substrate bias were almost the same with those under 0 V bias. However, under a negative (−5 V) substrate bias, the current decreased remarkably by Cl2adsorption and a high sensitivity was obtained. Moreover, the reaction rate constant was found to be about 10 times or more larger than those under 0 V and +5 V with positive biases. It was indicated that an external electric field affects the adsorption behavior of Cl2on SnO2surface. ©1996 American Institute of Physics.