In this letter we report on measurements of the diffusion coefficient for Ni in unrelaxed amorphous (&agr;) Si at temperatures between 270 and 435 °C using secondary ion mass spectrometry. A diffusion coefficient of ∼3×10−3 exp[−1.30(eV)/kT] cm2/s is obtained, which is approximately six to eight orders of magnitude lower than that for interstitial diffusion of Ni in crystalline (c) Si. The diffusion process in &agr;‐Si is described by a model invoking trap‐retarded interstitial migration; the main difference between the diffusion coefficients in &agr;‐Si andc‐Si is attributed to the presence of intrinsic traps in the amorphous phase with a binding enthalpy of ∼0.83 eV. ©1995 American Institute of Physics.