Current voltage (I-V-g) and deep level transient spectroscopy (DLTS) techniques have been carried out to study Schottky and ultraviolet oxidised Schottky diodes realised on n-type indium phosphide. For the oxidised structures, the ideality factor n versus voltage exhibits a peak around 0.2 V, from which the interface state density can be estimated to have a maximum value of 4 x 10(12) cm(-2) eV(-1). Comparable results for the same structures have been obtained from DLTS measurements. For the Schottky diodes, no peak appears in the plot of n versus voltage and no information on interface states can be deduced from I-V-g, measurements. However, DLTS measurements reveal an electrically active defect localised at the InP interface. This study shows that the I-V-g measurements may be used as a fast technique for interface states investigation.