The effects of surface preparation and illumination on electric parameters of Au/InSb/InP(100) Schottky diode were investigated, in the later diode InSb forms a fine restructuration layer allowing to block In atoms migration to surface. In order to study the electric characteristics under illumination, we make use of an He-Ne laser of 1 mW power and 632.8 nm wavelength. The current-voltage I(V-G), the capacitance-voltage C(V-G) measurements were plotted and analysed. The saturation current I-s, the serial resistance R-s and the mean ideality factor n are, respectively, equal to 2.03 x 10(-5) A, 85 Omega, 1.7 under dark and to 3.97 x 10(-5) A, 67 Omega, 1.59 under illumination. The analysis of I(V-G) and C(V-G) characteristics allows us to determine the mean interfacial state density N-ss and the transmission coefficient theta(n) equal, respectively, to 4.33 x 10(12) eV(-1) cm(-2), 4.08 x 10(-3) under dark and 3.79 x 10(12) eV(-1) cm(-2) and 5.65 x 10(-3) under illumination. The deep discrete donor levels presence in the semiconductor bulk under dark and under illumination are responsible for the non-linearity of the C-2(V-G) characteristic. (c) 2006 Published by Elsevier B.V.