In this paper, we propose a design approach for MEMS microphone that achieves SNR over 68 dB. Squeeze-film damping resistance was calculated for various diameter/pitch of acoustic holes arranged in backplate. Output noise level was estimated by equivalent circuit model. We show optimization method that considers capacitance change, process stability and mechanical robustness. Noise spectrum and SNR simulated by this method showed good agreement with experimental data. The results emphasize the importance of total optimization for MEMS-ASIC-package system. This design approach is expected to be applied to a variety of MEMS sensors that are susceptible to squeeze-film damping effect.