The Seebeck effect has been measured from liquid hydrogen temperatures into the intrinsic range for a series of single-crystal silicon samples in which varying concentrations of donor and acceptor atoms have been incorporated. Large values of Seebeck voltage believed to be caused by the type of phonon-electron coupling previously postulated as occurring in germanium have been found. This effect is found to be dependent upon charge carrier concentration, and upon sample dimension below 100\ifmmode^\circ\else\textdegree\fi{}K. A low-temperature reversal of the sign of the Seebeck voltage is observed for large carrier concentrations. It is understandable in terms of impurity band conduction. The behavior above room temperature into the intrinsic range is found to be consistent with electrical conductivity data.