This study has investigated a method for accurate analysis and design of shear horizontal surface acoustic wave (SH-SAW) sensors. The coupling of modes (COM) theory was used to develop an analytical model to satisfy Barkhausen's criteria for oscillation and avoid mode hopping. The theoretical simulation was highly consistent with the experimental results. The SH-SAW sensor presented here exhibited excellent reversibility, sensitivity, and repeatability when ammonia was at the ppb level.