A hybrid electrode array has been developed for use in an implantable MEMS-based cochlear prosthesis intended to restore hearing to the profoundly deaf. The array provides high-density stimulation and embedded position sensing to improve sound perception, minimize insertion damage, and optimize implant placement. Interfacing with a hermetically-packaged microcontroller and a bidirectional wireless interface over an eight-lead polymeric cable, the array integrates custom signal-processing electronics with thin-film lithographically defined IrO electrodes and polysilicon position sensors. The signal-processing chip (2.4 mm times 2.4 mm) operates from plusmn2.5 V, accepts 16-b commands, and performs command validation, stimulus current generation, site/sensor selection, offset compensation, and output-signal conditioning. The array contains nine polysilicon strain gauges to detect array position and tip contact. These strain sensors have gauge factors of 15-20, allowing the array tip position to be determined within 50 mum while providing tip-contact signals of more than 100 mV. The on-chip signal processing allows the use of a standard bus interface, reduces the parasitic capacitance and noise coupling on the connecting cables, allows the array shape to be imaged at a rate up to 10 times per second, and suppresses the output noise down to 3 mV.