The results of a photoemission study of the surface core-level shift of the Pb 5d level in the semiconductor PbS are reported. We found no surface shift within an experimental error of \ifmmode\pm\else\textpm\fi{}0.1 eV. Since this compound is highly ionic, this result is inconsistent with the theory that ionicity determines surface core-level shifts. However, the shift may be used to show that the heat of segregation of Bi in PbS is zero.