SiOxNy capped infrared rapid thermal annealing was investigated for activating high dose (≫7×1013 cm-2) Si implants in GaAs. The SiOxNy encapsulation resulted in enhancement in electrical activation. An electron concentration as high as 9×1018 cm-3 was obtained by 1120 °C, 5‐sec annealing using an SiOxNy encapsulant with 1.75 refractive index. Nonalloyed ohmic contacts were formed by depositing AuGe‐Ni on a heavily doped n‐type layer activated by this technique, where a 9×10-5 Ω cm2 specific contact resistance was obtained. Furthermore, low‐temperature (300 °C) alloying significantly improved a specific contact resistance to as low as 6×10-6 Ω cm2 while keeping a smooth morphology. These techniques, including low‐temperature alloying, are promising for GaAs and its heterostructure device applications.