The　paper　is　focused　on　the　investigation　of　fluid　flow　and　heat　transfer　characteristics　in　a　microchannel　heat　sink　with　offset　fan-shaped　reentrant　cavities　in　sidewall.　In　contrast　to　the　new　microchannel　heat　sink,　the　corresponding　conventional　rectangular　microchannel　heat　sink　is　chosen.　The　computational　fluid　dynamics　is　used　to　simulate　the　flow　and　heat　transfer　in　the　heat　sinks.　The　steady,　laminar　flow　and　heat　transfer　equations　are　solved　in　a　finite-volume　method.　The　SIMPLEX　method　is　used　for　the　computations.　The　effects　of　flow　rate　and　heat　flux　on　pressure　drop　and　heat　transfer　are　presented.　The　results　indicate　that　the　microchannel　heat　sink　with　offset　fan-shaped　reentrant　cavities　in　sidewall　improved　heat　transfer　performance　with　an　acceptable　pressure　drop.　The　fluid　flow　and　heat　transfer　mechanism　of　the　new　microchannel　heat　sink　can　attribute　to　the　interaction　of　the　increased　heat　transfer　surface　area,　the　redeveloping　of　the　hydraulic　and　thermal　boundary　layers,　the　jet　and　throttling　effects　and　the　slipping　over　the　reentrant　cavities.　The　increased　heat　transfer　surface　area　and　the　periodic　thermal　developing　flow　are　responsible　for　the　significant　heat　transfer　enhancement.　The　jet　and　throttling　effects　enhance　heat　transfer,　simultaneously　increasing　pressure　drop.　The　slipping　over　the　reentrant　cavities　reduces　pressure　drop,　but　drastically　decreases　heat　transfer.　(C)　2011　Elsevier　Ltd.　All　rights　reserved.