The thermal performance of Fabry–Perot InP lasers integrated onto different silicon photonics substrates by microtransfer printing is assessed. 500-μm-long ridge waveguide lasers on the original 350-μm-thick InP have an experimental thermal impedance, ZEXP, of 57 K/W that is reduced to 38 K/W after printing to a 500-μm-thick Si substrate. ZEXP for lasers printed on silicon-on-insulator wafers is ∼94 K/W, which is more than two times higher than that of the laser printed on the Si substrate. ZEXP of lasers printed on thermally insulating layers like benzocyclobutene (BCB) or SiO2 increases with the thickness of the layer. BCB adhesive layers as thin as 50 nm limit ZEXP to be greater than 55 K/W. The thermal properties for the different situations were modeled using finite-element simulations which confirmed the experimental results within 10% accuracy. The simulations show how changes in the geometry and the materials of the integration platform can influence the resulting thermal impedance.