In this work, the fabrication of gas sensors utilizing self-synthesized tungsten oxide nanowires (TONWs) and their response to NO 2 are reported. The gas sensor is based on a sputter-deposited WC x /SiO 2 /WC x triple-layer structure with the periphery of the SiO 2 layer etched chemically. Self-synthesized TONWs with crystalline W 18 O 49 (010) were grown by simple thermal annealing in nitrogen ambient, which linked, in parallel, the upper and lower WC x electrodes for gas sensing. The TONW-based sensors increased in resistance in NO 2 because the surface of TONWs comprised oxygen adsorbates and the adjacent space charge region was electron-depleted. The amount of enlargement in resistance increased with increasing temperature. To improve the detectability of the parallel-connected TONW-based sensor, a connection of several individual sensors in series was proposed to enlarge the number of TONWs for gas sensing. For the 8-series-connected sensor, a sensitivity as high as 9.3, a response time as low as about 9 s, and a detectability as low as 2 ppm for NO 2 were obtained.