The Schottky barrier height of NiAl/n-GaAs, NiAl/Al/Ni/n-GaAs, and Ni/Al/Ni/n-GaAs diodes has been studied by the current-voltage (I-V) and the capacitance-voltage (C-V) techniques. A NiAl alloy with 50 at. % Al was sputter deposited. An overall concentration of 50 at. % Al in NiAl/Al/Ni/n-GaAs contact structure, and two different overall concentrations of 25 and 60 at. % Al in Ni/Al/Ni/n-GaAs contact structure were prepared by sputter depositing different thicknesses of Ni and Al. An enhancement of the Schottky barrier height ranging from 0.1 to 0.13 eV was observed for each of the above contacts. The maximum barrier heights range from 0.95 to 0.98 eV for both the alloy and layered structure contacts, with ideality factors smaller than or equal to 1.1. The interfacial stability between the contacts and GaAs has been examined by cross-sectional transmission electron microscopy, glancing angle x-ray diffraction, and scanning Auger microscopy. A planar interface between contacts and GaAs was observed for both the alloy and layered contacts. A regrowth mechanism has been demonstrated to explain the enhancement of Schottky barrier height for these contacts.