The diffusion of implanted Be in liquid‐encapsulated Czochralski GaAs samples is modeled using SUPREM‐IV.GS, a simulator for GaAs and Si processing technology. The ‘‘plus one’’ approach for defect generation after implantation, as well as an assumption of local Ga interstitial sinks, are used to successfully simulate the high Be diffusivity, the uphill diffusion and the time‐dependent Be diffusivity. The fast diffusion of implanted Be can be simulated using the same intrinsic Be diffusivity as that used in the simulation of the slow diffusion of molecular beam epitaxy grown‐in Be. The roles of extended defects and nonequilibrium Ga point defects in the implanted Be anomalous diffusion behavior are taken into account. ©1995 American Institute of Physics.