Based on lasing wavelength red-shift of semiconductor lasers due to junction temperature rising in pulsed operations, time-resolved spectra were measured by adjusting Boxcar gate position related to the current pulse. The thermal relaxation times of TO-can and cm-Bar array AlGaAs laser were obtained to be 66 μs and 96 μs, respectively. The measured dynamic thermal characteristics are of significance for pumping solid-state lasers.