Titanium dioxide (TiO(2)) thin film gas sensors were fabricated via the sol-gel method from a starting solution of titanium isopropoxide dissolved in methoxyethanol. Spin coating was used to deposit the sol on electroded aluminum oxide (Al(2)O(3)) substrates forming a film 1 mu m thick. The influence of crystallization temperature and operating temperature on crystalline phase, grain size, electronic conduction activation energy, and gas sensing response toward carbon monoxide (CO) and methane (CH(4)) was studied. Pure anatase phase was found with crystallization temperatures up to 800 degrees C, however, rutile began to form by 900 degrees C. Grain size increased with increasing calcination temperature. Activation energy was dependent on crystallite size and phase. Sensing response toward CO and CH(4) was dependent on both calcination and operating temperatures. Films crystallized at 650 degrees C and operated at 450 degrees C showed the best selectivity toward CO. (C) 2010 Elsevier B.V. All rights reserved.