In this paper, 3-D, steady-state, analytical thermal models of high-power single-emitter semiconductor lasers (SEs) and laser diode arrays (LDAs) are derived, considering the heat conduction in multi-layered laser structures. Heat flow in the laser chips for an epi-down bonded SE and LDA is described using this model, and it is observed that the laser chips contribute to 8% and 6% of total heat dissipation for the SE and LDA, respectively. The submount size requirement for this model is discussed by revealing the heat flow in the submount. Through finite element simulations, the solution accuracy for the lasers with non-ideal submounts is confirmed. Finally, the performance of our proposed analytical models is verified by finite element simulations and experimental measurements based on the wavelength shift method. (C) 2019 Optical Society of America