We have studied the effect of a wet-chemical cleaning procedure and a thermal hydrogen treatment on Si-terminated 6H-SiC(0001) and C-terminated 6H-SiC(000 (1) over bar) surfaces by photoelectron spectroscopy and low-energy electron diffraction (LEED). On SiC(0001), the different steps of the wet-chemical treatment result in oxygen-contaminated surfaces with a monolayer of Si+ due to hydroxyl groups. The first step of the wet-chemical treatment also produces Si4+ accompanied by a (root3 x root3)R30 degrees LEED pattern, indicating the presence of areas terminated by a silicate adlayer on the surface. Annealing of SiC(0001) and SiC(000 (1) over bar) surfaces in molecular hydrogen at temperatures around 1000 degreesC removes surface oxygen and results in H-terminated surfaces with (1 x 1) periodicity, which are electronically and chemically passivated.