This study presents room-temperature ammonia (NH₃) selective gas sensors based on double-shell hierarchical SnO₂@polyaniline (PANI) composites. The sensors were fabricated using an in situ oxidative polymerization method, with the SnO₂ content adjusted to optimize sensing performance. The composite materials, denoted as DSPx, were synthesized by combining D-SnO₂ with PANI, resulting in a double-shell hierarchical structure that enhances gas sensing properties. The sensors were tested for NH₃ detection at room temperature, with the DSP20 sensor showing the best performance, achieving a response of 37.92 to 100 ppm NH₃, which is 5.1 times higher than that of a pure PANI sensor. The DSP20 sensor also demonstrated rapid response and recovery times, good repeatability, and long-term stability. The enhanced performance is attributed to the unique microstructure and the formation of a p-n heterojunction between the D-SnO₂ surface and PANI. The sensors were found to be selective for NH₃, with minimal response to other gases. The study highlights the potential of these composites for high-sensitivity, selective NH₃ detection at room temperature.This study presents room-temperature ammonia (NH₃) selective gas sensors based on double-shell hierarchical SnO₂@polyaniline (PANI) composites. The sensors were fabricated using an in situ oxidative polymerization method, with the SnO₂ content adjusted to optimize sensing performance. The composite materials, denoted as DSPx, were synthesized by combining D-SnO₂ with PANI, resulting in a double-shell hierarchical structure that enhances gas sensing properties. The sensors were tested for NH₃ detection at room temperature, with the DSP20 sensor showing the best performance, achieving a response of 37.92 to 100 ppm NH₃, which is 5.1 times higher than that of a pure PANI sensor. The DSP20 sensor also demonstrated rapid response and recovery times, good repeatability, and long-term stability. The enhanced performance is attributed to the unique microstructure and the formation of a p-n heterojunction between the D-SnO₂ surface and PANI. The sensors were found to be selective for NH₃, with minimal response to other gases. The study highlights the potential of these composites for high-sensitivity, selective NH₃ detection at room temperature.