An external cavity semiconductor laser that incorporates a large‐area amplifier has been successfully stabilized into a single transverse mode over the 600 &mgr;m width of the amplifier. Single‐transverse‐mode operation is achieved by using the combination of a diffractive mode‐selecting mirror and an aperture. 2.8 W of stable diffraction‐limited output power is achieved. ©1995 American Institute of Physics.