alpha-Sexithiophene (T6) thin films become smooth and featureless when annealed at temperatures above 160 degrees C. (The Figure shows a typical film before (left) and after (right) being annealed for 20 min at 170 degrees C.) This change in morphology is characterized in terms of the roughness exponent and it is suggested that the threshold temperature represents the onset of fast diffusion of T6 molecules on the surface.