The hyperfine coupling constants and electronic g-tensor were calculated for As-Ga(+) (antisite defect) in gallium arsenide using saturated cluster models and the density functional theory. The calculated values for the EPR parameters present an excellent agreement with the experimental results. For the hyperfine calculation, we evaluated the spin-polarization induced by the unpaired electron in order to observe the contribution of each electron to this parameter. (C) 2008 Elsevier B.V. All rights reserved.