We have applied ion channeling techniques to investigate effects of proton irradiation combined with thermal annealing on In–Ga atomic intermixing in a self-assembled InAs/GaAs quantum dot (QD) system. A molecular-beam-epitaxy grown InAs/GaAs QD sample was first irradiated with 1.0 MeV protons to a dose of 1014 cm-2 and subsequently annealed at temperatures between 300–700 °C. Ion channeling measurements indicate that such postgrowth processing leads to an enhanced amount of In atoms registering along the <100> growth direction. This observation yields direct evidence for the occurrence of In–Ga atomic intermixing in the QD structure during postirradiation annealing. The effective activation energy for such intermixing process is determined to be ∼0.2 eV. Furthermore, ion channeling data suggest three distinct stages for In–Ga atomic intermixing processes in the QD system, with In–Ga interdiffusion proceeding vertically along the growth direction or laterally in the QD layer, depending on postirradiation annealing temperatures.