Electrochemical sensing of biomolecules eliminates the need for bulky optical instruments required in traditional fluorescence-based sensing assays. Integration of the sensor interface electrodes and active electrochemical detection circuitry on CMOS substrates miniaturizes the sensing platform, enhancing portability for point-of-care applications, while enabling high-throughput, highly-parallel analysis. One embodiment includes a four-by-four active sensor array for multiplexed electrochemical biomolecular detection in a standard 0.25-μm CMOS process. Integrated potentiostats, including control amplifiers and dual-slope ADCs, stimulate the electrochemical cell and detect the current flowing through on-chip gold electrodes at each sensor site resulting from biomolecular reactions occurring on the chip surface. Post-processing techniques for fabricating biologically-compatible surface-electrode arrays in CMOS that can withstand operation in harsh electrochemical environments are described. Demonstrations showing example operation of the active CMOS array for biomolecular detection include cyclic voltammetry of a reversible redox species, DNA probe density characterization, and quantitative and specific DNA hybridization detection in real time.