We have performed an in situ depth profile study of Mn-doped GaN prepared by a low temperature thermal diffusion method using photoemission and x-ray absorption spectroscopy. It was revealed from the core-level photoemission measurements that Mn ions are diffused into a deep (∼70 Å) region of the GaN substrates and that the line shapes of Mn 3d partial density of states obtained by resonant photoemission measurements were close to that of Ga1−xMnxN thin films grown by molecular-beam epitaxy. From x-ray absorption spectroscopy and x-ray magnetic circular dichroism measurements at the Mn L edge, it was revealed that the doped Mn ions were in the divalent Mn2+ state and primarily paramagnetic. In magnetization measurements, weak hysteresis was detected in samples prepared using p-type GaN substrates while samples using n-type GaN substrates showed only paramagnetism.