We study the impact of improved heat removal on the performance of InGaAs/GaAs microdisk lasers epi-side down bonded onto a silicon substrate. Unlike the initial characteristics of microlasers on a GaAs substrate, the former’s bonding results in a decrease in thermal resistance by a factor of 2.3 (1.8) in microdisks with a diameter of 19 (31) µm, attributed to a thinner layered structure between the active region and the substrate and the better thermal conductivity of Si than GaAs. Bonded microdisk lasers show a 2.4–3.4-fold higher maximum output power, up to 21.7 mW, and an approximately 20% reduction in the threshold current. A record high 3 dB small-signal modulation bandwidth of 7.9 GHz for InGaAs/GaAs microdisk lasers is achieved.