In this paper, nitridation process of GaAs (1 0 0) substrates was studied in-situ using X-ray photoelectron spectroscopy (XPS) and ex-situ by means of electrical method I-V and photoluminescence surface state spectroscopy (PLS3) in order to determine chemical, electrical and electronic properties of the elaborated GaN/GaAs interfaces. The elaborated structures were characterised by I-V analysis. The saturation current I-s, the ideality factor n, the barrier height Phi(Bn) and the serial resistance R-S are determined. The elaborated GaN/GaAs structures are also exhibited a high PL intensity at room temperature. From the computer-aided analysis of the power-dependent PL efficiency measurements (PLS3 technique), the value of the interface state density N-SS(E) close to the mid-gap was estimated to be in the range of 2-4 x 10(11) eV(-1) cm(-2), indicating a good electronic quality of the obtained interfaces. Correlation among chemical, electronic and electrical properties of the GaN/GaAs interface was discussed. (c) 2005 Elsevier B.V. All rights reserved.