Ion beam mixing of In0.20Ga0.80As quantum well marker layers in GaAs following 1MeV Kr ion irradiation has been measured as a function of irradiation temperature and fluence. Secondary Ion Mass Spectrometry (SIMS) was used to measure the diffusion of the In0.20Ga0.80As layer following irradiation at various temperatures. Rutherford Backscattering (RBS) and channeling methods were used to determine the extent of the amorphization as a result of the implantation. The mixing parameter of the In0.20Ga0.80As in the GaAs matrix increased from approximately 120 angstroms5/eV at 77 K to approximately 160 angstroms5/eV in the temperature range of 300 K-450 K, but decreased somewhat at 573 K. This behavior of In0.20Ga0.80As marker layers will be compared to AlAs marker layers which show similar temperature dependence. These results are interpreted on the basis of thermal spikes and crystal structure.