The thermal properties of AlGaAs/GaAs laser diode bars have been analyzed in detail by transient thermal technique based on the diode forward voltage method on the vertical and horizontal thermal conduction paths, respectively. On the vertical thermal conduction path, it is found that the steady-state temperature rise of the central emitter among operated emitters has a linear relationship with the logarithm of the total operating current. The time constant determined for chip decreases with the total operating current, while the time constant determined for solder/heat sink interface and package remains almost constant. In addition, the effective thermal diffusivity of chip increases with total operating current. On the horizontal thermal conduction path, the time constant varies linearly with the distance increasing, and the effective thermal diffusivity remains almost constant. The results suggest that the thermal crosstalk between emitters increases with the total operating current. (C) 2012 Elsevier Ltd. All rights reserved.