Concentration-dependent Be diffusion in GaInP layers grown by gas source molecular beam epitaxy has been studied using secondary ion mass spectrometry. At a growth temperature of 500°C, apparent Be diffusion occurs at a doping level over 4 × 1019 cm-3. At lower temperature, the Be profile exhibits a significantly reduced diffusion. In contrast to Zn diffusion in metalorganic vapor phase epitaxy, no enhancement of Be redistribution in GaInP by adjacent n-type layers occurs. These results are explained based on the interstitial-substitutional diffusion model. A p+-n+ GaInP tunnel diode with a high reverse-biased conductance of 15 mA/cm2 at 1.7 mV has been achieved.