The emissivity of silicon wafers was measured for two specfic conditions. Firstly the emissivity of silicon wafers below 700 C was studied. Also the influence of front-side and back-side implantation on the emissivity was studied. It was found that a highly doped wafer or an epi-wafer with a higly doped bulk have a high emissivity which is independent of temperature. Secondly the influence of back-side roughness on emissivity was measured. It was shown the the intrinsic emissivity for a silicon wafer (outside the chamber) is merely changed for moderate roughnesses. On the other hand the effective emissivity inside a reflective chamber is sensitive to back-side roughness even for moderate roughnesses. Finally it was shown that wafers with an anti-reflective back-side layer (e. g. quarter wavelength oxide or oxinitride) behave like a nearly perfect black-body at the pyrometer wavelength. 1.