This study investigates the sensing performance of conductometric sensors for ammonia gas (NH₃) based on undoped and Ca-doped ZnO nanoparticles synthesized via the sol-gel process under supercritical dry ethanol conditions. The samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Fourier-transform infrared (FTIR) spectroscopy. All samples were found to be polycrystalline with a hexagonal wurtzite structure. TEM images showed that pure ZnO consisted of spherical nanoparticles, while Ca-doped ZnO had larger particles. The average crystallite sizes, calculated using the Williamson-Hall method, were 43, 80, and 96 nm for pure, Ca-1 at%, and Ca-3 at% samples, respectively. FTIR spectroscopy confirmed the formation of ZnO and the incorporation of calcium ions in the Ca-doped ZnO samples. The gas sensing performance of the Ca-doped ZnO sensor significantly improved, with a gas response (R₀/Rg) of 33 for 4000 ppm NH₃ at 300°C, showing good selectivity compared to CO, CO₂, and NO₂. The response and recovery times were 5 s and 221 s, respectively. The results indicate that Ca-doped ZnO has potential as a sensor material for ammonia detection due to its enhanced sensing performance and selectivity. The study also explores the sensing mechanism, showing that the interaction between the sensing material and NH₃ leads to a decrease in resistance due to the release of free electrons. The sensor demonstrated high selectivity for NH₃ compared to other gases, with the 1% Ca-doped ZnO sensor showing the best performance. The study concludes that Ca-doped ZnO is a promising material for ammonia gas detection due to its improved sensing properties and selectivity.This study investigates the sensing performance of conductometric sensors for ammonia gas (NH₃) based on undoped and Ca-doped ZnO nanoparticles synthesized via the sol-gel process under supercritical dry ethanol conditions. The samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Fourier-transform infrared (FTIR) spectroscopy. All samples were found to be polycrystalline with a hexagonal wurtzite structure. TEM images showed that pure ZnO consisted of spherical nanoparticles, while Ca-doped ZnO had larger particles. The average crystallite sizes, calculated using the Williamson-Hall method, were 43, 80, and 96 nm for pure, Ca-1 at%, and Ca-3 at% samples, respectively. FTIR spectroscopy confirmed the formation of ZnO and the incorporation of calcium ions in the Ca-doped ZnO samples. The gas sensing performance of the Ca-doped ZnO sensor significantly improved, with a gas response (R₀/Rg) of 33 for 4000 ppm NH₃ at 300°C, showing good selectivity compared to CO, CO₂, and NO₂. The response and recovery times were 5 s and 221 s, respectively. The results indicate that Ca-doped ZnO has potential as a sensor material for ammonia detection due to its enhanced sensing performance and selectivity. The study also explores the sensing mechanism, showing that the interaction between the sensing material and NH₃ leads to a decrease in resistance due to the release of free electrons. The sensor demonstrated high selectivity for NH₃ compared to other gases, with the 1% Ca-doped ZnO sensor showing the best performance. The study concludes that Ca-doped ZnO is a promising material for ammonia gas detection due to its improved sensing properties and selectivity.