An integrated optical/RF hybrid device was designed and fabricated for binary-phase-shift-keying (BPSK) subcarrier modulation. The device is composed of two identical high-speed multiple quantum well electroabsorption modulators branched with two multimode interference couplers. Using the device, we demonstrated that a RF subcarrier of 10 GI-Iz is directly modulated in a BPSK scheme with an independently applied RT carrier and digital signal.