A method for forming a three-dimensional, 3D, memory device, comprising: forming an alternating dielectric stack on a substrate ; forming a temporary top selective gate cut in an upper portion of the alternating dielectric stack and extending along a lateral direction; forming a plurality of channel holes penetrating the alternating dielectric stack ; removing the temporary top selective gate cut to form a trench ; and forming, simultaneously, a plurality of channel structures in the plurality of channel holes and a top selective gate cut structure in the trench , and wherein forming the plurality of channel structures in the plurality of channel holes comprises: before forming a functional layer , forming an epitaxial layer on a surface of the substrate that is exposed by the plurality of channel holes ; forming the functional layer covering the sidewall of each channel hole , the top surface of the epitaxial layer in each channel hole , as well as the sidewalls and the bottom surface of the trench ; characterized by forming a protecting layer to cover the functional layer ; and removing portions of the functional layer and the protecting layer on the bottom of each channel hole to form a first recess that exposes or extends into the epitaxial layer , wherein the protecting layer is completely removed. forming an alternating dielectric stack on a substrate ; forming a temporary top selective gate cut in an upper portion of the alternating dielectric stack and extending along a lateral direction; forming a plurality of channel holes penetrating the alternating dielectric stack ; removing the temporary top selective gate cut to form a trench ; and forming, simultaneously, a plurality of channel structures in the plurality of channel holes and a top selective gate cut structure in the trench , and wherein forming the plurality of channel structures in the plurality of channel holes comprises: before forming a functional layer , forming an epitaxial layer on a surface of the substrate that is exposed by the plurality of channel holes ; forming the functional layer covering the sidewall of each channel hole , the top surface of the epitaxial layer in each channel hole , as well as the sidewalls and the bottom surface of the trench ; characterized by forming a protecting layer to cover the functional layer ; and removing portions of the functional layer and the protecting layer on the bottom of each channel hole to form a first recess that exposes or extends into the epitaxial layer , wherein the protecting layer is completely removed. before forming a functional layer , forming an epitaxial layer on a surface of the substrate that is exposed by the plurality of channel holes ; forming the functional layer covering the sidewall of each channel hole , the top surface of the epitaxial layer in each channel hole , as well as the sidewalls and the bottom surface of the trench ; characterized by forming a protecting layer to cover the functional layer ; and removing portions of the functional layer and the protecting layer on the bottom of each channel hole to form a first recess that exposes or extends into the epitaxial layer , wherein the protecting layer is completely removed. <EOS>