A novel P-P isotype heterojunction sensor was developed by modifying microstructure silicon array(MSSA) with self-assembled polyaniline (PANI) nano-thin film for ammonia (NH3) detection at room temperature, and the comparative study of response performance was focused on sensors with varied etching time of MSSA. The results indicated that PANI nanorods network was successfully deposited on MSSA surface, and PANI/MSSA sensor exhibited superior NH3-sensing properties than PANI/plane silicon sensor, which should be ascribed to three-dimensional structure and p-p heterojunction enhancement effect. Meanwhile, the optimized sensor with 4 min etching time exhibited high response, good reversibility, repeatability and selectivity when exposed to NH3. (C) 2014 Elsevier B.V. All rights reserved.