The　delamination　of　layered　crystals　that　produces　single　or　few-layered　nanosheets　while　enabling　exotic　physical　and　chemical　properties,　particularly　for　semiconductor　functions　in　optoelectronic　applications,　remains　a　challenge.　Here,　we　report　a　facile　and　green　approach　to　prepare　few-layered　polymeric　carbon　nitride　(PCN)　semiconductors　by　a　one-step　carbon/nitrogen　steam　reforming　reaction.　Bulky　PCN,　obtained　from　typical　precursors　including　urea,　melamine,　dicyandiamide,　and　thiourea,　are　exfoliated　into　few-layered　nanosheets,　while　engineering　its　surface　carbon　vacancies.　The　unique　sheet　structures　with　strengthened　surface　properties　endow　PCNs　with　more　active　sites,　and　an　increased　charge　separation　efficiency　with　a　prolonged　charge　lifetime,　drastically　promoting　their　photoredox　performance.　After　an　assay　of　a　H2　evolution　reaction,　an　apparent　quantum　yield　of　11.3　%　at　405　nm　was　recorded　for　the　PCN　nanosheets,　which　is　much　higher　than　those　of　PCN　nanosheets.　This　delamination　method　is　expandable　to　other　carbon-based　2D　materials　for　advanced　applications.　©　2017　Wiley-VCH　Verlag　GmbH　&　Co.　KGaA,　Weinheim