A correlation was established between the morphological structure of the Si surface caused by chemical preparation and its electronic interface properties by combined monitoring of (i) the surface roughness and hydrogen and oxide coverage by ex situ (UV-VIS-IR) and in situ (UV-VIS) spectroscopic ellipsometry (SE), and (ii) the density D-it,D-min and energetic distribution D-it(E) of interface states by surface photovoltage (SPV) measurements. With these systematic investigations a wet-chemical H-termination procedure was optimized and very smooth Si(lll) surfaces without any native oxide coverage were prepared, characterized by an intrinsic surface state distribution and a very low surface state density D-it,D-min < 1.5 x 10(10) cm(-2) eV(-1). On these surfaces the resonant absorption due to the SI-H bonds was directly observed by infrared ellipsometry.