A novel three-dimensional(3D) hierarchical structure and a roughly oriented one-dimensional(1D) nanowire of WO_3are selectively prepared on an alumina substrate by an induced hydrothermal growth method.Each hierarchical structure is constructed hydrothermally through bilateral inductive growth of WO_3 nanowire arrays from a nanosheet preformed on the substrate.Only roughly oriented 1D WO_3 nanowire can be obtained from a spherical induction layer.The analyses show that as-prepared 1D nanowire and 3D hierarchical structures exhibit monoclinic and hexagonal phases of WO_3,respectively.The gas-sensing properties of the nanowires and the hierarchical structure of WO_3,which include the variations of their resistances and response times when exposed to NO_2,are investigated at temperatures ranging from room temperature(20 ℃) to 250 ℃ over 0.015 ppm-5 ppm NO_2.The hierarchical WO_3 behaves as a p-type semiconductor at room temperature,and shows p-to-n response characteristic reversal with the increase of temperature.Meanwhile,unlike the1 D nanowire,the hierarchical WO3 exhibits an excellent response characteristic and very good reversibility and selectivity to NO_2 gas at room temperature due to its unique microstructure.Especially,it is found that the hierarchical VO_3-based sensor is capable of detecting NO_2 at a ppb level with ultrashort response time shorter than 5 s,indicating the potential of this material in developing a highly sensitive gas sensor with a low power consumption. A novel three-dimensional (3D) hierarchical structure and a roughly oriented one-dimensional (1D) nanowire of WO_3are selectively prepared on an alumina substrate by an induced hydrothermal growth method. Ecch hierarchical structure is constructed hydrothermally through bilateral inductive growth of WO_3 nanowire arrays from a nanosheet preformed on the substrate. Once roughly roughly oriented 1D WO_3 nanowire can be obtained from a spherical induction layer. the analyzes show that as-prepared 1D nanowire and 3D hierarchical structures exhibit monoclinic and hexagonal phases of WO_3, respectively. gas-sensing properties of the nanowires and the hierarchical structure of WO_3, which include the variations of their resistances and response times when exposed to NO_2, are investigated at temperatures ranging from room temperature (20 ° C) to 250 ° C over 0.015 ppm-5 ppm NO_2. hierarchical WO_3 behaves as a p-type semiconductor at room temperature, and shows p-to-n response characteristic reversal wit h the increase of temperature. Meanwhile, unlike the 1 D nanowire, the hierarchical WO3 exhibits an excellent response characteristic and very good reversibility and selectivity to NO 2 gas at room temperature due to its unique microstructure. Especially, it is found that the hierarchical VO_3-based sensor is capable of detecting NO 2 at a ppb level with ultrashort response time shorter than 5 s, indicating the potential of this material in developing a highly sensitive gas sensor with a low power consumption.