Dynamic feedback properties of a 1.55 μm InAs/InP quantum dash laser are reported. The ground state linewidth enhancement factor (αH-factor) is found to be enhanced from ∼ 1 to ∼ 14 as the bias current is increased beyond the threshold value. As a consequence of the variation in the αH-factor, the feedback sensitivity of the quantum dash semiconductor laser is dramatically affected over the entire range of operational currents. The onset of its critical feedback regime, which is incompatible with data transmission, is shown to exhibit a variation of approximately 20 dB for the quantum dash device.