Surface roughness of a silicon wafer heated at 800 to 1100 degrees C under atmospheric pressure in hydrogen ambient is studied. Haze of the surface becomes intense as the heating temperature is decreased. However, haze of the surface does not appear when the native oxide film on the silicon surface is completely removed. Atomic force microscopy images show that the surface heated at 900 degrees C has many small pits whose shapes depend on the crystal plane, that is, squares for the (100) plane and triangles for the (111) plane. The pits are formed due to the difference in the chemical reaction rates between hydrogen-silicon and hydrogen-silicon dioxide. Small areas of bare silicon surf ace caused by the incomplete removal of the native oxide film are etched by hydrogen gas at a faster rate than the native oxide islands. The behavior of surface roughness with pressure and heating time agrees well with that predicted by the pit formation model in this study.