This paper presents the hardware realization and modeling of high-density microelectrode arrays including both microelectronic readout amplifiers as well as three-dimensional microelectrodes forming a fully integrated CMOS compatible system enabling research in electrophysiology. The presented chip offers the highest density of microprobes, reported in literature, all of which can be accessed through on-chip amplifiers, using a time-multiplexing scheme. An accurate model of the electrode interface including noise performance is also presented.