The influence of different surface treatments on the device characteristics of Schottky rectifiers was investigated. Prior to the formation of Schottky barrier contacts the SiC surface was either thermally annealed in hydrogen, etched using O2 or CF4/Ar/H2 as reactive gases or Ar sputtered. Differences in reverse current densities of several orders of magnitude for different surface treatments were observed. The effective device area was determined by the optical beam induced current (OBIC) technique. The results confirm that the effective device area is given by the area of the metal contact and the additional area of the surface charge induced depletion layer. Our results indicate the importance of an optimized surface treatment in order to control the quality and the area of the surface region for achieving optimum device performance.