A method for producing and singulating a wafer stack, each wafer of the wafer stack comprising one or more integrated circuit dies , each wafer comprising a semiconductor substrate and a functional layer on at least one side of the substrate, the dies being defined by delimited portions of the functional layer (1a,1b;49a,49b) and of the substrate , wherein the wafer stack is produced by : • one or more steps of directly bonding a first wafer to a second wafer, wherein functional layer portions of one or more dies of the first wafer are bonded respectively to functional layer portions of one or more dies of the second wafer, so as to form a wafer stack comprising one or more stacks of bonded dies, and • after the direct bonding steps, forming a top layer on the wafer stack comprising on top of the stacks of bonded dies, one or more contact structures electrically connected to an underlying stack of bonded dies, and wherein : • prior to each direct bonding step, intermediate singulation streets (10a,10b;52a,52b) are produced on the facing surfaces of two wafers that are to be bonded together, by removing the material of the functional layers from the facing surfaces, in areas which circumvent a central portion of a die , • prior to each direct bonding step, the method comprises the step of aligning the intermediate singulation streets of the facing surfaces of the two wafers to be bonded, • all of the intermediate singulation streets in the stacks of bonded dies formed in the wafer stack being aligned to each other, • after fabrication of the top layer of the wafer stack, an upper singulation street is produced in the top layer for each stack of dies formed in the wafer stack, by removing the materials of the top layer from an area of the top layer, the upper singulation street being aligned with the previously produced intermediate singulation streets , • after the formation of the upper singulation street , the wafer stack is singulated by etching the semiconductor substrates of the wafer stack in the areas corresponding to the aligned intermediate and upper singulation streets , thereby obtaining one or more singulated die stacks . • one or more steps of directly bonding a first wafer to a second wafer, wherein functional layer portions of one or more dies of the first wafer are bonded respectively to functional layer portions of one or more dies of the second wafer, so as to form a wafer stack comprising one or more stacks of bonded dies, and • after the direct bonding steps, forming a top layer on the wafer stack comprising on top of the stacks of bonded dies, one or more contact structures electrically connected to an underlying stack of bonded dies, • prior to each direct bonding step, intermediate singulation streets (10a,10b;52a,52b) are produced on the facing surfaces of two wafers that are to be bonded together, by removing the material of the functional layers from the facing surfaces, in areas which circumvent a central portion of a die , • prior to each direct bonding step, the method comprises the step of aligning the intermediate singulation streets of the facing surfaces of the two wafers to be bonded, • all of the intermediate singulation streets in the stacks of bonded dies formed in the wafer stack being aligned to each other, • after fabrication of the top layer of the wafer stack, an upper singulation street is produced in the top layer for each stack of dies formed in the wafer stack, by removing the materials of the top layer from an area of the top layer, the upper singulation street being aligned with the previously produced intermediate singulation streets , • after the formation of the upper singulation street , the wafer stack is singulated by etching the semiconductor substrates of the wafer stack in the areas corresponding to the aligned intermediate and upper singulation streets , thereby obtaining one or more singulated die stacks . <EOS>