In this paper, a novel microring resonator (MRR)-assisted Mach-Zehnder interferometric (MZI) structure to operate as an electro-optic half adder utilizing the optical switching phenomenon of Si-MRR is proposed. The proposed device has two Si-MRRs with dual inputs, used in the tandem configuration in the lower and upper arms of an MZI structure. An externally controllable optical ‘π’ phase shifter is also incorporated in one of the arms of the MZI. The carrier-injected forward-biased PIN waveguide structure is incorporated into the ring resonator architecture to achieve the extinction ratio (ER) tunability. For the proposed electro-optic adder, −1.85 V and +2 V are considered as logic 0 and 1, respectively. One of the output terminals will emulate an optical AND gate providing the carry bit (CB), while the other output terminal will emulate an optical EX-OR gate offering the sum bit (SB). The proposed device was modeled and simulated using MATLAB. The simulation results estimate the simulated static ER of the SB and CB is 27.44 dB and 18.08 dB, respectively. To demonstrate the proposed device’s efficacy, two 10 Gb/s PRBS input streams at 1550 nm were used, and the time domain simulation results indicate a successful electro-optic half adder suitable for photonic integrated circuits (PICs).