The aim of this work is to evaluate the reliability issues of mid-power white LEDs subjected to high-temperature operating conditions. Four families of devices, picked from four different leading manufacturers, have been submitted to a series of active stresses in environmental chambers with ambient temperatures ranging from 45 °C to 105 °C. The experimental data, collected during the first 4000 hours of stress, revealed the presence of multiple degradation phenomena: a) a decrease of the luminous flux for LED junction-temperatures above 120 °C; b) the worsening of the electrical characteristics of the devices; c) the worsening of the chromatic properties of the emitted light. The temperature-related kinetics of the degradation processes, which were generally found to be thermally activated, helped to provide a first insight into reliability of mid-power LEDs for lighting applications.