Thermal management is one of the most important issues for today's microelectronics design. Photonics is expected to bring significant advantages to future beyond-CMOS microprocessors in terms of heat dissipation with the use of optical interconnects but thermal management of integrated laser sources remains an issue. In this paper, we investigate the thermal properties of various III-V semiconductor laser sources integrated on silicon. Monolithic (through GaSb epitaxy) and heterogeneous (through InP/SOI bonding) integration approaches are studied with both ridge and microresonators laser geometries. It is first shown that the presence of dislocations in monolithically integrated structures, as determined by transmission electron microscopy, have no impact on thermal conductivities. Thermal mappings of the devices are then computed. It is demonstrated that heterogeneous lasers are thermally more insulated from the surrounding CMOS than monolithic lasers (especially at the back side), which avoids photonic-induced hot spots formation on the chip, but can degrade the overall laser performances.