The thermal stability of Schottky diode parameters of the fabricated MIS and intimate Ni/n-LEC GaAs Schottky diodes have been investigated using current-voltage (I-V) techniques after being annealed in the range of 100-600 degrees C for 5 min in N-2 atmosphere. It has been seen that the intimate device is thermally mure stable than the MIS device. The I-Ii characteristics of the MIS device were deteriorated after 400 degrees C, while those of the intimate device, after 600 degrees C. This has been attributed to the fact that the MIS Ni/n-LEC GaAs SBDs heated from 100 degrees C to 400 degrees C suffers from problems arising from the native oxide layer formed on the GaAs surface. Thus, it has been concluded that a reacted contact is thermodynamically stable in the absence of the native oxide layer than an unannealed one or than MIS diodes up to a given annealing temperature. Furthermore, we have evaluated the equilibrium interface charge density and the interface state charge density distribution from the forward bias I-V characteristics of the diodes which show MIS diode behavior before and after annealing. The results have supported our interpretations related to the ideality factor and Schottky barrier height. (C) 1998 Elsevier Science B.V. All rights reserved.