A preferred conformal penetrating multi electrode array includes a plastic substrate that is flexible enough to conform to cortical tissue. A plurality of penetrating semiconductor micro electrodes extend away from a surface of the flexible substrate and are stiff enough to penetrate cortical tissue. Electrode lines are encapsulated at least partially within the flexible substrate and electrically connected to the plurality of penetrating semiconductor microelectrodes. The penetrating semiconductor electrodes preferably include pointed metal tips. A preferred method of fabrication permits forming stiff penetrating electrodes on a substrate that is very flexible, and providing electrical connection to electrode lines within the substrate.