Be diffusion from 0.2μm Be doped (3×10 19 cm −3 ) In 0.53 Ga 0.47 As layer sandwiched between 0.5μm undoped In 0.73 Ga 0.27 As 0.58 P 0.42 layers, grown by GSMBE has been studied. The samples were subjected to RTA in temperature range from 700°C to 900°C with time durations of 10–240s. SIMS was employed for a quantitative determination of the Be depth profiles. Two kick-out models of substitutional–interstitial diffusion have been considered. To explain the obtained experimental results, the kick-out model, involving neutral Be interstitial species and singly positively charged Ga or In self-interstitials is proposed. The built-in electric field, bulk self-interstitial generation/annihilation, the Fermi-level and extended defect formation effects were taken into account in the simulations.