A compact four channel RF/optical subcarrier multiplexed (OSCM) transmitter MMIC has been implemented in a commercial 0.6 /spl mu/m GaAs MESFET process. The designed MMIC consists of four voltage controlled oscillators (VCO) with a frequency range of 3.8-5.5 GHz for subcarrier generation and four modulators for on-off keying (OOK) subcarrier modulation. This MMIC supports up to 200 Mb/s data rate per each channel. This transmitter IC occupies a die area of 120/spl times/120 mil/sup 2/. We present design and characterization of the first fully monolithic four channel transmitter IC for multichannel OSCM link applications.