Characteristics of a compact III V optocoupler heterogeneously integrated on a silicon substrate and formed by a 31 um in diameter microdisk (MD) laser with a closely-spaced 50 um × 200 um waveguide photodetector are presented. Both optoelectronic devices were fabricated from the epitaxial heterostroctructures with InGaAs/GaAs quantum well-dot layers. The measured dark current density of the photodetector was as low as 2.1 uA cm?2. The maximum link efficiency determined as the ratio of the photodiode photocurrent increment to the increment of the microlaser bias current was 1% 1.4%. The developed heterogeneous integration of III V devices to silicon boards by Au-Au thermocompression bonding is useful for avoiding the difficulties associated with III V epitaxial growth on Si and facilitates integration of several devices with different active layers and waveguides. The application of MD lasers with their lateral light output is promising for simplifying requirements for optical loss at III V/Si interface.