With the advent of implantable hearing aids, the implementation and acoustic sensing strategy of the implantable microphone becomes an important issue. Previously, implantable microphones were inserted under the skin, which causes loud noise signals from touching or moving the skin. In this reported work, mounting a microphone in a drilled hole to the middle ear cavity is proposed. This method does not cause any skin movement problems or aesthetic problems. Furthermore, surgical operation is easy because the microphone can be mounted onto the drilled bone and does not need to be clipped or attached to the ossicular chain. From guinea pig experiments (n = 5), the loss of transmission from the proposed microphone observed was only 1.17 ± 0.36 and 5.04 ± 0.84 dB (mean ± std.) for the 0.2-1 and 3-4 kHz bands. The lowest minimum detectable sound pressure was measured as 27.7 dB SPL (SNR: 6 dB) at 3150 Hz without pinna or canal effects.