The goal of the present project is to develop intracochlear acoustic receivers (ICAR’s) for measurement of the sound pressure in the inner ear of human temporal bones and in acute large animal experiments. In addition, the ICAR is designed to be used as an implantable microphone for totally implantable cochlear implant (TICI) systems. The presented ICAR concept is based on a commercially available MEMS condenser microphone customized with a protective diaphragm providing sealing properties and optimized sensor head geometry for accessing the tiny fluid-filled cavities of the human inner ear. The first ICAR prototypes (PT I) have been used for numerous intracochlear sound pressure measurements in human and sheep temporal bones. The data thus obtained are in good agreement with the literature. The second ICAR prototype (PT II) was further adapted for surgical insertion in the scala tympani in acute large animal experiments. First experiments have been successfully performed and further revealed that the presented ICAR concept is a suitable receiver technology for TICI systems. Currently, the development of a fully biocompatible ICAR (PT III) is ongoing. This sensor must fulfill all important requirements of a TICI device such as high performance, low power consumption and good system integration.