In this paper, a novel strain-induced quantum well intermixing (QWI) technique is employed on InGaP/InAlGaP material system to promote interdiffusion via application of a thick-dielectric encapsulant layer, in conjunction with cycle annealing at elevated temperature. Broad area devices fabricated from this novel cost-effective QWI technique lased at room-temperature at a wavelength as short as 608nm with a total output power of ~46mW. This is the shortest- wavelength electrically pumped visible semiconductor laser, and the first report of lasing action yet reported from post- growth interdiffused process. Furthermore, we also demonstrate the first yellow superluminescent diode (SLD) at a wavelength of 583nm with a total two-facet output power of ~4.5mW - the highest optical power ever reported at this wavelength in this material system. The demonstration of the yellow SLD without complicated multiquantum barriers to suppress the carrier overflow will have a great impact in realizing the yellow laser diode. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.