Micro/nano　structures　on　the　Cu　substrate　are　normally　used　for　the　enhancing　the　heat　transfer　capacity　for　many　boiling-related　applications.　Conventional　methods　for　fabricating　these　structures,　however,　require　additional　processing　equipment　and　involve　relatively　complex　processes.　In　this　study,　a　simple　immersion　method　for　generating　in-situ　micro/nanocrystal　structures　on　Cu　substrates　is　developed　for　simplifying　the　fabrication　with　reduced　cost　and　improving　the　boiling　performance　in　the　meantime.　Using　characterization　analytical　instruments　including　SEM,　AFM,　XRD,　EDS　and　XPS,　the　surface　morphology　and　chemical　contents　of　the　micro-　and　nanocrystals　generated　on　the　Cu　substrate　were　examined.　The　experimental　results　showed　that　the　hierarchical　micro/nanocrystals　enabled　simultaneous　enhancements　in　critical　heat　flux　(CHF)　and　heat　transfer　coefficient　(HTC),　indicating　the　superiority　of　the　hierarchical　micro/nanocrystals　in　facilitating　the　boiling　performance　compared　to　conventional　structured　surfaces.　It　is　found　that　the　nanosheet　and　micro-flowers　(NSMF)　surface　provides　the　largest　enhancement　amongst　other　micro/　nano　structures　including　the　nanograss　forests　(NG),　nanograss　forests　and　micro-petals　(NGMP),　and　nanograss　forests　and　micro-flowers　(NGMF).　Comparatively,　the　CHF　and　HTC　could　achieve　65.7　W/cm2　and　4.9　W/cm2K,　showing　an　increase　of　the　CHF　and　HTC　by　56.5　%　and　170　%,　respectively,　using　the　smooth　surface　in　the　same　condition　as　the　benchmark.　It　is　implied　that　the　liquid　circulation　is　apparently　promoted　through　the　separation　of　vapor–liquid　pathway　and　the　bubble　blanket　formation　is　remarkably　inhibited　due　to　the　special　structure　and　morphology　of　the　hierarchical　surface.　However,　vital　factors　including　the　surface　wettability　and　the　experimental　accuracy　need　to　be　considered　for　optimizing　the　boiling　performance　in　diverse　scenarios.　©　2023　Elsevier　Inc.