Cr₂O₃ thick films were fabricated by screen printing method on alumina substrates and annealed at 700 ℃, 800 ℃, and 900 ℃ in air, respectively. Structural properties examined by XRD and SEM showed (116) dominant Cr₂O₃ peak and increased grain sizes with the annealing. The resistance of the films decreased with increasing the annealing temperature. Gas sensing characteristics to NH3, CO, C₄H_(10), and NO gases showed sensitivity only to NH3 gas. Cr2O3 thick films annealed at 700 ℃ had the sensitivity of about 15 % for 100 ppm NH₃ gas at the working temperature of 300 ℃. The thick films had good selectivity to the NH₃ gas. The response time to NH₃ gas was about 10 seconds.