Partial and arc discharge in gas insulated switchgear (GIS), such as a switching component or circuit breaker, can lead decomposition gas generation of sulphur hexafluoride (SF6), which is generally used as an electrical insulation medium. The authors had demonstrated that SF6 decomposition products, such as HF, SO2, SOF2, can be detected by using a carbon nanotube (CNT) gas sensor, which was fabricated by dielectrophoresis. In this study, we selected carbon tetrafluoride (CF4) as a target decomposition gas to be detected by nanomaterial-based gas sensors. Because CF4 is hard to be removed by using a molecular sieve or absorbent, the decomposition product accumulates in a long time and can be used for GIS diagnosis. Three kinds of semiconducting nanomaterial, carbon nanotube, SnO2 nanoparticle, ZnO nanowires, were integrated on a microelectrode by dielectrophoresis respectively to fabricate a gas sensor. It was found that SnO2 gas sensor showed the highest response to CF4 gas at 1% concentration in SF6. The conductance of the SnO2 sensor gradually decreased with elapsed time after exposure to the CF4 gas depending on the operating temperature.