Broad stripe semiconductor lasers and laser arrays are capable of generating high optical output powers, but the transverse mode structure is generally poor. Two ways of improving the transverse mode structure by integrating spatial mode filters within the semiconductor lasers are discussed. Firstly, the far-field pattern of 980 nm broad area lasers has been improved by placing passive, low-loss slab waveguides on either side of the active region. Control devices exhibited a broad far-field spectrum (10 degree(s)) containing several peaks. Lasers with passive slab waveguides on both sides of the active region exhibited a single peak in the far-field spectrum, the divergence of which decreased as the length of the passive sections was increased. Secondly, novel antiguided arrays lasers have been fabricated by processes which are free of epitaxial regrowth stages. The operation of antiguided array lasers is dependent on the creation of an effective refractive index step between the antiguide core and the interelement regions. We describe the fabrication of five-element antiguided laser arrays at 1.48 micrometers in which undoped passive waveguiding layers have been added to the standard laser design. These waveguides significantly alter the shape of the far field emission from the lasers, showing that the array elements are pulled in-phase with each other. We also describe a second technique, using zinc diffusion to disorder a superlattice cladding layer, for creating the necessary index step in a ten-element antiguided laser array operating at 0.860 micrometers . Output powers approach 400 mW per facet into a 3(DOT) (FWHM) beam.