Hydrogen cleaning and nitridation of InSb (100) using radio frequency (r.f.)-generated radicals was investigated using reflection high energy electron diffraction (RHEED), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Hydrogen cleaning was found to remove antimony oxide and carbon contamination even at room temperature (RT) by creating volatile species but did nor remove the indium oxide. Hydrogen cleaning at 275 degrees C gave a clean, flat surface which showed a (4 X 2) In-rich reconstruction, while hydrogen cleaning at temperatures above the maximum congruent temperature of similar to 325 degrees C resulted in a surface with a step-terrace structure accompanied by large islands and deep pits. By annealing to 375 degrees C a surface cleaned at 275 degrees C, a surface with a step-terrace structure but no pit or island defects could be obtained. Similar behaviour was observed for nitrided rather than oxidised surfaces.