In this work, we report a novel fabrication approach for highly porous SnO2 microwires using a semi-closed thermal evaporation system under controlled low-pressure conditions. The unique microstructure of the syn thesized microwires, characterized by nanoscale porosity and high crystallinity, was achieved by tuning the deposition pressure between 0.85 and 1.15 Torr. While demonstrated with SnO2, this approach applies to a wide range of metal oxides, including single, binary, and doped systems. Unlike conventional open or VLS-based deposition methods, this system enables precise morphological control via thermal evaporation under tunable pressure conditions, promoting a vapor-solid (VS) growth mechanism. Structural and morphological charac terizations confirmed that lower pressure enhances defect density and grain boundary formation, which are critical to gas sensing behavior. The SnO2 microwires were integrated into a conductometric gas sensor and evaluated for NO2 detection. The optimized sensor exhibited a high response of 2900 % to 2 ppm NO2 at a low operating temperature of 100 ◦C, along with excellent selectivity against interfering gases such as H2, H2S, and CO. The enhanced sensing performance is attributed to the synergistic effects of grain boundary modulation, Schottky barrier formation at the Pt/SnO2 interface, and catalytic activation near the contacts. This study demonstrates the potential of porous SnO2 microwires as a promising material for low-temperature, selective NO2 sensing in environmental monitoring applications