Micro Electro Mechanical System (MEMS) technology is used in a bio-electrode for measuring electrocorticography (ECoG) signals in Sprague Dawley (SD) rats. The electrical signal in the rat brain is evoked by auditory stimulation and can be detected with newly developed bioelectrode sensors. A back-end system can record signals from eighteen positions. One signal was used as the ground signal, and one was used as the reference signal. The average results for 100 samples revealed the relationship between temporal resolution and spatial resolution of sixteen positions in the brain. The bioelectrode was fabricated with two parylene layers (10um, 1um) to cover the platinum metal wires. Oxygen plasma is used to etch the bioelectrode and to define a stable size and shape in production of batches of electrodes. To simplify implantation, the bioelectrode was designed to fit the curvature of SD rat head bones, and a special connector was used to transmit signals to the back-end system, which successfully recorded Auditory Evoked Potentials (AEP) signals after implant surgery.