While describing the electrical transport using single parabolic model, it was mentioned in a couple of papers that a negative value of reduced chemical potential (u0) implies that Fermi level (EF) resides inside the band. I have read the definition of 'u' as being u=EF-E/KbT, where E is the conduction band minima or valence band maxima. I am not able to deduce the relation between sign of 'u' and its position from the above. Can someone help me understand vividly ?