The electronic band structures, partial and total spin density of states of Cr, Fe, Mn and Ni doped β-Ga 2 O 3 are studied. It is shown that there exists only one spin polarized state around the Fermi level for all doped β-Ga 2 O 3 . Ferromagnetism is predicted for Mn and Ni doped while spin-glass ground states are predicted for Cr and Fe doped β-Ga 2 O 3 . All doped β-Ga 2 O 3 exhibits intermediate bands which are filled with only one spin state electrons and isolated from valence and conduction bands due to the splitting of the 3d orbitals by the potential of crystal and spin interaction