The method of tuning the wavelength of a quantum well laser to a shorter emission wavelength is accomplished by the step of thermal annealing the laser for a prescribed period of time, the length of the period and the temperature of annealing being based upon what primary emission wavelength is desired. For good results, the annealing is conducted in an elemental anti-outdiffusion environment or the laser structure to be annealed is encapsulated so that any outdiffusion of laser elemental constituents is discouraged during thermal annealing. In an exemplary illustration of the invention, laser heterostructures of the GaAl/GaAlAs regime are utilized and annealed for several hours in an As environment to selectively reduce the emission wavelength by as much as 20. or more. The As environment prevents the outdiffusion of As from the GaAl GaAlAs heterostructure during thermal annealing, elemental As having the lowest temperature of vaporization of elemental Ga, Al and As. High temperature annealing above this temperature may tend to drive elemental As from the heterostructure thereby changing its operating characteristics. Thermal annealing may be carried out in an annealing furnace, generally sealed in a quartz ampoule, or in a thermal pulse annealing system wherein properly prepared wafer samples may be alternately heated uniformly for prescribed periods of time at predetermined temperatures and periodically checked to determine the amount emission wavelength shift as compared to the set emission wavelength desired to be achieved for the laser.