The magnetic property of GaMnAs can be enhanced by increasing the Mn concentration as well as hole concentration. The interstitial Mn is inevitably formed when Mn concentration is very high even if the growth condition is carefully controlled. They act as a double donor and compensates for Mn acceptors in GaAs. The interstitial Mn atoms also tend to be bound by those occupying the substitutional Ga site. The combination of interstitial and substitial Mn atom produces antiferromagnetic pairs. In order to reduce the interstitial Mn and increase hole concentration, we introduce Mn delta-doped layers separated by undoped GaAs layers. The magnetic properties are investigated as a function the spacing between Mn delta-doped layers. It is found that magnetization characteristics such as the magnetic susceptibility, coercive force and Curie temperature are enhanced when the spacing between Mn delta-doped layers is optimized. (c) 2007 Elsevier B.V. All rights reserved.