In　this　work,　we　proposed　a　porous-wall　(PW)　microchannel　heat　sink,　in　which　micro　pin　fin　arrays　were　fabricated　on　sidewalls　of　rectangular　microchannels　by　MEMS　(Microelectrical　Mechanical　System)　technique.　High　speed　flow　visualizations　were　performed　simultaneously　with　heat　transfer　and　pressure　drop　measurements　to　investigate　the　flow　boiling　characteristics　of　PW　microchannel　heat　sink.　Conventional　rectangular　(Rec)　microchannel　heat　sink　was　also　explored　together　as　a　comparison.　Experiments　were　carried　out　with　pure　acetone　liquid　at　inlet　temperature　of　30　degrees　C,　mass　flux　from　255　kg/(m(2).s)　to　843　kg/(m(2).s),　heat　flux　from　4　W/cm(2)　to　110　W/cm(2)　and　the　maximum　vapor　quality　at　the　outlet　of　the　channel　was　0.88.　Experimental　results　demonstrated　that　the　PW　microchannels　reduce　wall　superheat　of　onset　of　nucleate　boiling　(ONB)　and　improve　critical　heat　flux　(CHF)　compared　to　the　Rec　microchannels.　Moreover,　the　PW　microchannels　show　significant　heat　transfer　enhancement,　pressure　drop　reduction　and　mitigation　of　two-phase　flow　instability.　The　porous　walls　provide　numerous　nucleation　sites　and　the　intensive　pin　fins　arrangements　introduce　significant　wicking　effect　to　maintain　the　liquid　rewetting,　which　contribute　to　the　above　notable　flow　boiling　enhancement.　(C)　2018　Elsevier　Ltd.　All　rights　reserved.