The faceting of tips of twin plates in the interior of grains under annealing in phosphorus-doped polysilicon films, produced by low-pressure chemical vapor deposition, has been investigated by transmission electron microscopy. It has been shown that the facet types and number of facets depend on the annealing temperature. The stability diagram for the different facet types has been constructed. Three kinds of faceting transitions that take place on the twin tips have been studied. The transformation of curved grain boundary into a gain boundary facet with increasing temperature has been observed for the first time. (C) 2013 The Authors. Published by Elsevier B.V. All rights reserved.