Inductively coupled plasma reactive ion etching is used to fabricate the monolithic beam splitter in silicon-on-insulator wafer. The near-field image shows that the symmetric 1x2 T-branch works well. The rms roughness of the corner mirror surfaces is measured by atomic force microscope, and the sidewall surface roughness of rib waveguide is evaluated by the corner mirror rms roughness. The scattering losses from the rough sidewall surfaces and the rough mirror surfaces are evaluated to be 0.5 dB/cm and 0.2 dB/mirror, respectively. And the fiber-waveguide insertion loss is measured approximately 5.0 dB.