The article explores the essential role of lattice oxygen in hydrogen sensing reactions, challenging the conventional understanding that surface chemisorbed oxygen is the primary contributor. Using in-situ characterizations and density functional theory (DFT) calculations, the study demonstrates that lattice oxygen actively participates in hydrogen sensing. Germanium-doped tin dioxide (SGO) is used as a case study, revealing that lattice oxygen is involved in the sensing process. DFT calculations show that the p-band center of oxygen plays a critical role in enabling lattice oxygen participation in hydrogen sensing. SGO exhibits high response (S = 39.2 for 500 ppm H2), good selectivity, and fast response speed, indicating the significance of lattice oxygen in enhancing gas-sensing performance. The study provides experimental evidence and theoretical support for a new sensing mechanism where lattice oxygen contributes to the sensing process, offering insights into the design of high-performance gas-sensing materials. The findings highlight the importance of understanding the role of lattice oxygen in metal oxide semiconductors for developing efficient hydrogen sensors.The article explores the essential role of lattice oxygen in hydrogen sensing reactions, challenging the conventional understanding that surface chemisorbed oxygen is the primary contributor. Using in-situ characterizations and density functional theory (DFT) calculations, the study demonstrates that lattice oxygen actively participates in hydrogen sensing. Germanium-doped tin dioxide (SGO) is used as a case study, revealing that lattice oxygen is involved in the sensing process. DFT calculations show that the p-band center of oxygen plays a critical role in enabling lattice oxygen participation in hydrogen sensing. SGO exhibits high response (S = 39.2 for 500 ppm H2), good selectivity, and fast response speed, indicating the significance of lattice oxygen in enhancing gas-sensing performance. The study provides experimental evidence and theoretical support for a new sensing mechanism where lattice oxygen contributes to the sensing process, offering insights into the design of high-performance gas-sensing materials. The findings highlight the importance of understanding the role of lattice oxygen in metal oxide semiconductors for developing efficient hydrogen sensors.