A new method is presented for determining the semiconductor-laser linewidth-broadening factor α. Measurements on 1.5 μm devices suggest that α decreases with decreasing laser length. 300 μm-long devices emitting at 1.3 and 1.5 μm were found to have similar values of α (6.6 cf. 6 4), but at 0.85 μm significantly lower results were measured (2.8)