The electrical properties of single crystal 4H-SiC thin films have been investigated using the Au-Schottky barrier diodes (SBD's) on the etched surfaces in SF6/O-2 plasma with reactive ion etching mode. It is found by atomic force microscopy (AFM) that the root-mean-square (RMS) roughness of etched surfaces was reduced from 8.5Angstrom to 5.7Angstrom as oxygen concentration in the reactant gases increased from 0% to 50%. From the Auger electron spectroscopy (AES), it was revealed that the reactive ion etching (RIE) etched surfaces had the residual species such as fluorine and oxygen regardless of etching conditions. The I-V characteristics of SBD's showed that an increase of oxygen content in the SF6/O-2 feeding gas mixtures made an improvement in the reverse-bias performance of Schottky diodes in spite of such residual contaminants on the surface.