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A method is described for the manufacture of a three-dimensional electrode array geometry for chronic intracortical stimulation. This silicon based array consists of a 4.2*4.2*0.12 mm thick monocrystalline substrate, from which project 100 conductive, silicon needles sharpened to facilitate cortical penetration. Each needle is electrically isolated from the other needles, and is about 0.09 mm thick at its base and 1.5 mm long. The sharpened end of each needle is coated with platinum to facilitate charge transfer into neural tissue. The following manufacturing processes were used to create this array: thermomigration of 100 aluminum pads through an n-type silicon block, creating trails of highly conductive p + silicon isolated from each other by opposing pn junctions; a combination of mechanical and chemical micromachining which creates individual penetrating needles of the p + silicon trails; metal deposition to create active electrode areas and electrical contact pads; and array encapsulation with polyimide.