A　novel　grooved　flat　plate　heat　pipe　(FPHP)　was　designed.　The　grooved　structure　of　the　FPHP　can　improve　its　axial　and　radial　heat　transfer　and　also　can　form　the　capillary　loop　between　condensation　and　evaporation　surfaces.　From　experiment,　we　also　obtained　the　best　filling　amount　of　this　grooved　FPHP.　By　comparing　the　thermal　resistance　of　a　solid　copper　plate　with　that　of　the　FPHP,　it　is　suggested　that　the　critical　heat　flux　condition　should　be　maintained　to　use　FPHP　as　efficient　thermal　spreaders　for　electronics　cooling.