Silicon-based thin-film technology has been used to develop high-density cochlear electrode arrays with up to 32 sites and four parallel channels of simultaneous stimulation. The lithographically-defined arrays utilize a silicon-dielectric-metal-parylene structure with 180 microm-diameter IrO sites on 250 microm centers. Eight on-board strain gauges allow real-time imaging of array shape during insertion, and a tip sensor measures forces on any structures contacted in the scala tympani (e.g., the basilar membrane). The array can be pre-stressed to hug the modiolus, which provides position reference. Tip position can be resolved to better than 50 microm. Circuitry mounted on the base of the array generates stimulating currents, records intra-cochlear responses and position information, and interfaces with a custom microcontroller and inductively-coupled wireless interface over an eight-lead ribbon cable. The circuitry delivers biphasic 500 microA current pulses with 4 microA resolution and a minimum pulse width of 4 micros. Multiple sites can be driven in parallel to provide higher current levels. Backing structures and articulated insertion tools are being developed for dynamic closed-loop insertion control.