A new design of microelectromechanical systems (MEMS) condenser microphone employing silicon carbide (SiC) diaphragm is proposed for the sonic detection. The sensing structure consists of SiC thin film as the top plate and perforated Si as the back plate. The numerical analysis and simulation studies compare the mechanical performances of the square-shape SiC diaphragm. Four parameters are considered i.e. resonance frequency, cutoff frequency, maximum deflection and maximum stress. The theoretical and simulated results match closely. Overall, the 680 μm × 680 μm SiC diaphragm with the thickness of 1.00 μm gives the optimized mechanical performances for the sonic detection.