Integrated external cavity GaAs/AlGaAs single quantum well lasers were fabricated by selective quantum well disordering. Lasers with 2.07‐mm‐long passive sections and 0.48‐mm‐long active sections had threshold currents of 33 mA, compared to 9.8 mA for lasers without passive sections. Lasing data indicate a residual modal loss of 11 cm−1in the passive sections, consistent with direct waveguide loss measurements. Control composite structures with a nondisordered quantum well in the passive sections showed significantly higher threshold currents and a large red shift of as much as 11.4 nm in the lasing wavelength compared to lasers without a passive cavity. This red shift is the main reason for the reduced resonant losses in integrated external cavity lasers with a nondisordered quantum well in the passive section.