The results from two novel experimental techniques to investigate the influence of thermal effects on large aperture, high power semiconductor lasers are presented. The first technique is achieved via fabricated micro-stripe heating elements, integrated onto the laser diode using standard photolithographic technology. The second involves focusing an Ar+ beam onto the injection stripe of a standard broad-area laser to investigate the effect of localized heating. Results from both experiments show that the internal temperature distribution has a pronounced influence on the near- and far-fields of large aperture semiconductor lasers. By tailoring this distribution, significant improvements to near- and far-fields can be obtained.