The linewidth enhancement factor &agr; in an InGaAs/InP strained‐layer multiple quantum well (MQW) laser emitting near 1.55 &mgr;m has been determined from the spontaneous emission spectra below threshold. The active layers in the MQW structure in this device are under 0.7% compressive strain. The measured &agr; at the lasing wavelength is 2.0. The calculation of &agr; using interpolated bandstructure parameters shows that it varies rapidly with injected carrier density and the calculated value for our device is close to the measured value. The small &agr; for strained MQW InGaAs lasers should result in performance improvement that are advantageous for lightwave system application.