A　three-dimensional　numerical　model　of　the　interrupted　microchannel　heat　sink　is　presented　to　study　the　effects　of　pressure　drop　and　heat　transfer　characteristics　due　to　various　dimensions　and　positions　of　rectangular　ribs　in　the　transverse　microchambers.　For　the　first　part　of　the　optimum　analysis,　the　rib　length　and　width　are　chosen　as　the　geometry　variables　to　find　their　optimum　dimensions.　As　to　the　second　part　of　the　present　analysis,　two　arrangement　variables　including　the　distance　from　the　parallel　microchannels　to　the　rib　row　and　the　space　between　two　adjoining　transverse　microchambers.　In　addition,　the　fluid　flow　and　heat　transfer　mechanisms　of　the　newly　proposed　microchannel　heat　sink　are　analyzed.　Finally,　based　on　the　thermal　enhancement　factor　performance　maps,　the　optimal　dimension　and　position　parameters　of　the　rectangular　ribs　are　obtained　in　principle.　©　2012　Elsevier　Ltd.　All　rights　reserved.