Mg-doped p-InxGa1-xN (0 less than or equal to x less than or equal to 0.045) and p-AlyGa1-yN (0 less than or equal to y less than or equal to 0.095) layers were grown on sapphire substrates by metalorganic chemical vapor deposition (MOCVD). We investigated the activation energy of Mg dopant in Mg-doped p-InGaN, p-GaN and p-AlGaN, as confirmed by PL emission lines of the band to impurity transition of free electrons with neutral Mg acceptors. Under the same Mg doping concentration of 2 x 10(19) cm(-3), the band to acceptor emission energy E(e(-), A(0)) of Mg-doped p-type InxGa1-xN decreased with increasing the In composition, whereas the E(e(-), A(0)) of Mg-doped p-type AlyGa1-yN increased with Al composition. It suggests that the activation energy of Mg dopant has proportional relationship with the band gap energy of III-nitrides. The Hall measurements showed that the hole concentration of Mg-doped p-type In0.045Ga0.955N was 1.3 x 10(18) cm(-3) and that of Mg-doped p-type Al0.075Ga0.925N was 8.9 x 10(16) cm(-3). (C) 2004 Elsevier B.V. All rights reserved.