GaAs has recently received attention due to the potential use of Mn-doped material in spintronics applications. Mn Ga both magnetically and electrically dopes the material, and, in order to increase the control over the materials properties, selective passivation by hydrogen has been suggested. However, some debate exists over the location of H in Mn Ga-H complexes. We have examined the energetics, structure and vibrational modes of Mn Ga-H complexes in GaAs. In addition, we have examined the properties of Mn-H complexes in InP, where the vibrational modes have been detected, and GaN, which is also of interest for spintronics applications and exhibits enhanced magnetisation subsequent to hydrogenation. For GaAs and InP, H lies at the bond-centre, whereas in GaN H anti-bonds to N. In all cases Mn is electrically passivated by H, but retains the high spin ground state required for magnetic material.