A novel structure for chronically implantable cortical electrodes using new Benzocyclobutene (BCB) biopolymer was devised, which provides both flexibility for micro-motion compliance between brain tissues and skull and stiffness for better surgical handling. BCB is very attractive polymer for stable long-term implant function, because it has flexibility, biocompatibility, low moisture uptake (> 0.2 wt%), and low dielectric constant (~2.6). For easy operation during surgical insertion, a 5~10?m thick silicon backbone layer is attached to the desired region of the electrode to increase the stiffness. It is then followed by 1 mm of flexible part of the electrode without silicon backbone layer designed to absorb stress from any micro-motion between the brain tissue and the electrode. The fabricated implants have tri-shanks with 5 recording sites (20 x 20?m) and 2 vias (40 x 40?m) on each shank. BCB electrodes with 5?m and 10?m thick backbone silicon penetrated pia of rat brain without buckling.