Crystalline (1 11) and amorphous silicon surfaces have been studied by scanning tunnelling microscopy. An orientated, reproducible, corrugated structure has been observed on Si ( 11 1) surfaces. The voltage dependence of the corrugation amplitude may be attributable to surface states. The surfaces of amorphous silicon thin films show some reproducible structure in the range of a few tens of hgstriims, observable only when the applied voltage between the tip and sample is between -1.3 and +0*4V.