Assessment of surface arsenic coverage during epitaxial growth of n-type doped Si is essential to the understanding of dopant incorporation and segregation behaviour. This particular problem is investigated using reflectance anisotropy spectroscopy (RAS) and reflection high energy electronic diffraction (RHEED) intensity oscillation technique as in situ probes. Initial measurement and analysis show that RAS is extremely sensitive to the presence of As on vicinal Si(0 0 1) surfaces and that the changes in the RA response at 2.6 eV are approximately linear to the As surface coverage produced by repeated cycles of low temperature adsorption of arsine followed by thermal desorption of hydrogen. For singular Si(0 0 1)surfaces where RAS cannot be applied, RHEED intensity oscillations were used to follow the change in As surface concentration during the growth of an Si capping layer over pre-deposited As. Using a model of the influence of As on the Si growth rate from Si hydrides, a surface As concentration profile was obtained and compared with that predicted by a model of As surface segregation. The results were in good agreement with secondary ion mass spectrometry measurements of a similar sample.