The　flat　two-phase　thermosyphon　is　placed　between　the　heat　source　and　the　heat　sink,　which　can　achieve　the　uniform　heat　flux　distribution　and　improve　the　performance　of　heat　sink.　In　this　paper,　a　two-dimensional　heat　and　mass　transfer　model　for　a　disk-shaped　flat　two-phase　thermosyphon　is　developed.　By　solving　the　equations　of　continuity,　momentum　and　energy　numerically,　the　vapor　velocity　and　temperature　distributions　of　the　flat　two-phase　thermosyphon　are　obtained.　An　analysis　is　also　carried　out　on　the　ability　of　flat　two-phase　thermosyphon　to　spread　heat　and　remove　hot　spots.　In　order　to　observe　boiling　and　condensation　phenomena,　a　transparent　flat　two-phase　thermosyphon　is　manufactured　and　studied　experimentally,　The　experimental　results　are　compared　with　numerical　results,　which　verify　the　physical　and　mathematical　model　of　the　flat　two-phase　thermosyphon.　In　order　to　study　the　main　factors　affecting　the　axial　thermal　resistance　of　two-phase　thermosyphon,　the　temperatures　inside　the　flat　two-phase　thermosyphon　are　measured　and　analyzed.　(C)　2008　Elsevier　Ltd.　All　rights　reserved.