Gas sensing properties of pure and Fe modified SnO2 thin films deposited by rheotaxial grown and thermal oxidation (RGTO) method have been investigated. Modification of SnO2 surface with Fe results in an improved and selective response towards H2S. Sensor films containing 0.64 at % Fe exhibited a sensor response of 14.5 towards 10 ppm of H2S at 225 degrees C with a response and recovery time of 90 and 98 s, respectively. Long term stability measurements indicate that the sensor response is stable over a measured period of 35 days. X-ray photoelectron spectroscopy analysis indicates that Fe exists in the form of Fe3O4 over the SnO2 sensor surface. An improved response towards H2S is attributed to the formation of low band gap FeS upon interaction of Fe3O4 with the H2S. A gas sensing mechanism has been proposed using the results of sensing characteristics, x-ray photoelectron spectroscopy and work function measurements. (C) 2015 Elsevier B.V. All rights reserved.