Extreme-long (up to 70 mm) Si neural multielectrodes are presented for the first time. Probes with different shaft lengths (15-70 mm) were formed by deep reactive ion etching and have been equipped with Pt recording sites of various configurations. In vivo measurements on rodents indicated good mechanical stability, robust implantation and targeting capability, and high quality signals from different locations of the cerebrum have been recorded. The accompanied tissue damage was characterized by histology. With platinum electroplating, electrical impedance reduction was achieved, the improved charge transfer capability was characterized by cyclic voltammetry.