We report on the crystal structures, magnetic and magnetotransport properties of epitaxial (Ga 1 - x Mn x )N films with low Mn concentration (x=0.06-0.5%) grown by plasma-enhanced molecular beam epitaxy, exhibiting n-type conductivity and ferromagnetism with Curie temperature in the range 550-700K. Transmission electron microscopy studies revealed that Mn ions substitute for Ga ions in the epitaxial structure, leading to the expansion of the lattice parameter a of the hexagonal (wurtzite) structure. The temperature dependence of the sheet resistance is found to show negative magnetoresistance in the temperature range 4-300K, indicative of ferromagnetic semiconducting (Ga,Mn)N films.