The development of simple and reproducible synthesis techniques for obtaining one-dimensional semiconducting nanostructures is essential for the advancement of gas sensor devices. We report a facile and versatile approach for the in-situ growth of vertically oriented hematite nanorods to be applied as a resistive ozone gas sensor. The α-Fe2O3 nanorods were grown via a hydrothermal treatment directly onto an Al2O3 substrate with interdigitated Pt electrodes, thus facilitating the integration of nanorods into the sensing platform. At 150 °C, the gas-sensing experiments revealed a good sensitivity of these nanorods to different ozone concentrations (10 to 570 ppb), besides a fast response time and repeatable response–recovery cycles. The present study offers a promising way for designing high-performance gas sensors based on hematite nanorods.