It is experimentally shown for the first time that far field lobe broadening, which is a multilateral mode operation under continuous wave operation in phased array lasers that emit diffraction limit beams under pulsed conditions mainly originates from temperature distribution along the junction plane. Spectrally resolved near field measurements show that pulse width, where broadening occurs, corresponds well to the one where temperature influence appears. Moreover, measurement of temperature distribution by the near field measurements and laser Raman spectroscopy show that a considerable temperature difference does exist between the center and edge elements in the array.