GaAs quantum well (QW) lasers with distributed Bragg reflection (DBR) Al0.3Ga0.7As/GaAs superlattice gratings have been fabricated by the single‐step, maskless focused ion beam (FIB) mixing. 200 keV Si++FIB implantation with a beam diameter of ∼60–70 nm and a dose of 1014cm−2was used to obtain localized compositional mixing. The DBR grating period was 350 nm, corresponding to a third order grating matched to the emission from the 30 nm wide QW. Lasing operation was examined by optical pumping. With a pumping power 1.6× the threshold value, lasing modes were observed near 827 nm, with a spacing of 3 A˚ and a linewidth of 1.5 A˚. ©1995 American Institute of Physics.