A single-chip micromachined microphone is proposed to meet the requirement of small size, high performance, and low cost. It consists of a rigid perforated backplate, a floating diaphragm, air gaps, an acoustic chamber, and a silicon substrate. The simply supported diaphragm can be achieved by using two sacrificial layers. The sacrificial material is phosphor-silicate glass, and sacrificial layers are etched away to form the air gaps. The KOH etching solution is used to fabricate the acoustic chamber in pyramidal shape. The simply supported diaphragm has the larger mechanical compliance than that of clamped diaphragm. The electro-acoustical sensitivity of the simply supported structure has at least 5.72 times larger than that of clamped structure. Although there are many parameters can increase electro-acoustical sensitivity, the simply supported diaphragm is one of the most effective approaches. Bias voltage can be used to increase sensitivity, and it creates the electrostatic force on the diaphragm. The dominative parameter of diaphragm deflections changes from sound pressure to the electrostatic force, when bias voltage is larger than 2.3 V. A microbeam is used to support a floating diaphragm, and the microbeam determines the resonance modes. The natural resonance frequency should locate outside the telephony band. When the width of the microbeam is small, the lateral vibration will appear early and result in the natural resonance frequency.