In　this　work,　flow　boiling　pressure　drop　characteristics　based　on　the　hydrodynamic　instability　with　deionized　water　on　the　micro-pin-finned　surfaces　in　a　horizontal　narrow　microchannel　with　a　hydraulic　diameter　of　952　µm　were　investigated.　The　micro-pin-finned　surfaces　can　be　divided　into　three　types　based　on　the　size　and　arrangement　of　the　fins　(A30-120/S30-120/A50-120).　The　experiments　were　conducted　under　the　mass　flux　from　200　to　500　kg/m2s　and　the　inlet　temperature　of　30　to　50　.　The　two-phase　flow　patterns　on　the　micro-pin-finned　surfaces　were　captured　by　a　high-speed　camera.　The　flow　boiling　instabilities　in　the　microchannel　are　studied,　and　the　two-phase　flow　pattern,　wall　temperature,　heat　fluxes　and　mass　fluxes　as　well　as　pressure　drop　are　observed　and　analyzed.　The　experiment　results　show　the　mass　flux　has　a　significant　effect　on　the　pressure　drop,　while　it　has　almost　no　change　with　the　increasing　heat　flux　in　the　microchannel　heat　sink　during　the　nucleate　boiling.　Besides,　the　pressure　drop　of　the　A30-120　and　S30-120　surfaces　is　less　than　that　of　smooth　surface　due　to　the　effect　of　hydrophobic　surface　and　bubble　drag　reduction.　The　maximum　pressure　drop　of　the　A30-120　surface　is　only　0.970　kPa　corresponding　to　the　mass　flux　and　critical　heat　flux　(CHF)　of　500　kg/m2s　and　341.4　W/cm2　in　this　study,　respectively.　And　the　overall　performance　of　the　micro-pin-finned　surfaces　is　also　evaluated　in　the　microchannel　heat　sink,　which　can　achieve　more　than　a　30%　reduction　in　pressure　drop　and　thermal　resistance　compared　with　the　smooth　surface.　©　2022　Elsevier　Ltd