S1O2 layers, ∼ 15 nm thick, were formed on Si (100), (110), and (111) surfaces by a low-temperature, 200–300°C, plasma-assisted oxidation/deposition process sequence. The distribution of the trap density at the S1O2/Si interface, and in the Si band-gap, Dit, was deduced from capacitance-voltage, C-V, measurements. The values of Dit at midgap varied with crystal orientation in a similar way as in thermally grown oxides. In addition, the low-temperature oxides displayed a characteristic and intrinsic dangling bond state, the so-called Pb center, at ∼0.3 eV above the Si valence-band edge. Samples exposed to atomic H prior to the oxidation and deposition steps, showed an increase in Dit due to a roughening of the Si surfaces, which produced additional broad bands of defect states, at ∼0.5 and ∼0.7 eV above the Si valence-band edge.