The development of WO₃-based gas sensors for analysis of acetone in exhaled breath is significant for noninvasive diagnosis of diabetes. A series of Fe-doped hexagonal and monoclinic WO₃ phase−junction (Fe−h/m−WO₃) sensors were synthesized by the hydrothermal calcination method, and the influences of operating temperature and light irradiation on the response were studied. Under light emitting diode (LED) illumination, Fe−h/m−WO₃ exhibited higher responses to acetone than those of the undoped WO₃-based sensors at an operating temperature of 260 °C with 90% relative humidity, and good linearity between response and acetone concentration (0.5 to 2.5 ppm) was achieved under the 90% relative humidity condition. Meanwhile, the optimal Fe−h/m−WO₃ sensor exhibited high selectivity and stability for a duration of three months. The excellent sensing performance of Fe−h/m−WO₃ was attributed to the formation of phase−junction and Fe doping, and these were beneficial for the separation of photon−generated carriers and oxygen adsorption on the WO₃ surface, promoting the generation of superoxide radicals, which was demonstrated by electron paramagnetic resonance and photocurrent tests. Additionally, the Fe−doped WO₃ phase−junction sample also showed good photocatalytic performance for rhodamine B degradation. This study may provide some insights into rational design of new types of gas sensors and offer an alternative for noninvasive diagnosis of diabetes.