In this paper the gallium oxide thin film oxygen gas sensor operated at the high temperature over 900 degreesC has been analyzed. Gallium oxide thin films have been deposited by sputtering method using a powder target instead of a ceramic target. The sensing characteristics, sensitivity and response time of the sensor has been studied. Crystallinity and composition of the produced films have been evaluated by XRD and AES. The sensing characteristics of the sensor for oxygen gas response were measured at 1000 degreesC. The results of the film obtained from a powder target show lower in resistance, higher in sensitivity and faster in gas response rate in comparison with those obtained from a ceramic target. AFM measurements have been done to observe the surface of thin film. It has been found that there are differences in size of grain due to different sputtering conditions and targets. It is also shown that oxygen gas response, depend on the grain size and surface structure of the materials. A very fast and normal rate rising time has been estimate by the combination of a surface contact model and bulk contact model. The simulation results are compared with the experimental measured data. A good qualitative agreement is found with them. (C) 2003 Elsevier Science B.V. All rights reserved.