Disclosed herein are an apparatus for electrically assessing and/or manipulating cells. One aspect is directed to electrically mapping cells on the surface of the semiconductor substrate via cross-electrode impedance measurements. Further according to some aspects, the electrode array allows for spatially addressable electrical stimulation and/or recording of electrical signals in real-time using the CMOS circuitry. Some of these aspects are directed to using an electrode array to perform cell patterning through electrochemical gas generation, and extracellular electrochemical mapping.