A power module comprising a base plate , an electronic module disposed on the base plate via a substrate and a cooling device ; the cooling device comprising: a heat sink surface having at least one cooling segment disposed therein comprising: an inlet plenum for entry of a cooling medium ; a plurality of inlet manifold channels coupled orthogonally to the inlet plenum for receiving the cooling medium from the inlet plenum ; a plurality of outlet manifold channels disposed parallel to the inlet manifold channels ; and an outlet plenum coupled orthogonally to the plurality of outlet manifold channels for exhaust of the cooling medium ; and a plurality of millichannels disposed in a plate surface orthogonally to the inlet and the outlet manifold channels ; wherein the plurality of millichannels direct the cooling medium from the plurality of inlet manifold channels to the plurality of outlet manifold channels ; the plurality of millichannels is formed in the base plate , the millichannels each have a width and a height on the order of millimeters in each dimensions, characterized in that a prefabricated heat sink plate comprising the at least one cooling segment disposed in the heat sink surface is detachably coupled to the base plate such that the plate surface of the base plate overlaps the heat sink surface , wherein the heat sink plate includes a seal disposed surrounding the at least one cooling segment ; and the inlet plenum is disposed parallel to the outlet plenum , and the entry of the cooling medium into the inlet plenum and the exhaust of the cooling medium from the outlet plenum are along a same direction. a heat sink surface having at least one cooling segment disposed therein comprising: an inlet plenum for entry of a cooling medium ; a plurality of inlet manifold channels coupled orthogonally to the inlet plenum for receiving the cooling medium from the inlet plenum ; a plurality of outlet manifold channels disposed parallel to the inlet manifold channels ; and an outlet plenum coupled orthogonally to the plurality of outlet manifold channels for exhaust of the cooling medium ; and an inlet plenum for entry of a cooling medium ; a plurality of inlet manifold channels coupled orthogonally to the inlet plenum for receiving the cooling medium from the inlet plenum ; a plurality of outlet manifold channels disposed parallel to the inlet manifold channels ; and an outlet plenum coupled orthogonally to the plurality of outlet manifold channels for exhaust of the cooling medium ; and a plurality of millichannels disposed in a plate surface orthogonally to the inlet and the outlet manifold channels ; wherein the plurality of millichannels direct the cooling medium from the plurality of inlet manifold channels to the plurality of outlet manifold channels ; the plurality of millichannels is formed in the base plate , the millichannels each have a width and a height on the order of millimeters in each dimensions, characterized in that a prefabricated heat sink plate comprising the at least one cooling segment disposed in the heat sink surface is detachably coupled to the base plate such that the plate surface of the base plate overlaps the heat sink surface , wherein the heat sink plate includes a seal disposed surrounding the at least one cooling segment ; and the inlet plenum is disposed parallel to the outlet plenum , and the entry of the cooling medium into the inlet plenum and the exhaust of the cooling medium from the outlet plenum are along a same direction. <EOS>