We report on the motional dynamics of Mu(-) and the ionization processes related to the Mu(T) acceptor state in n-type gallium phosphide. Muon spin resonance results on semi-insulating GaP suggest the presence of both Mu(+) and Mu(-) diamagnetic states above similar to 400 K. From the growth step in the RF amplitudes, we obtain an energy of similar to 0.82 eV for the Mu(T) acceptor-related hole ionization. The loss of the Mu- RF-component above 600 K yields an energy of similar to 1.7eV, which is assigned to thermal promotion of an electron from Mu- to the conduction band. These two results locate the Mu(T) acceptor level with respect to the valence and conduction band edges, respectively. Low-field spin precession and zero-field depolarization data on n-type GaP show a peak in diamagnetic fraction below 300 K, and a roughly linear increase in amplitude at higher temperatures. (c) 2008 Elsevier B.V. All rights reserved.