Micro-electro-mechanical-system (MEMS) based microphones have grown remarkably in recent years. Their performance has been improving and approaching laboratory standard microphones. One of the challenges that MEMS microphones are facing is to achieve high sensitivity combined with low equivalent input noise (EIN). EIN in dB(A) indicates the lowest A-weighted acoustic pressure level that a microphone can detect relative to 20 µPa under atmospheric pressure. This paper discusses the measurement method, its setup and the associated measurement uncertainty for the EIN of MEMS microphones. The measurement method has been validated that it can reproduce the EIN at 13.61 dB(A)±0.88 dB for a LS2F reference microphone, whose EIN is specified at 14 dB(A) in its manufacturer’s data sheet. The measurement setup can potentially measure EIN near 0 dB(A) provided that a good anechoic environment can be achieved. The MEMS microphone under test is able to deliver EIN at 43.61 dB(A)±1.08 dB.