A thermosiphon includes a condenser; an evaporator that includes a fluid channel and a heat transfer surface, the heat transfer surface defining a plurality of fluid pathways in the fluid channel that extend through the fluid channel, the evaporator configured to thermally couple to one or more heat-generating electronic devices; and a transport member that fluidly couples the condenser and the evaporator, the transport member including a liquid conduit that extends through the transport member to deliver a liquid phase of a working fluid into the fluid pathways, the transport member further including a surface to vertically enclose the plurality of fluid pathways.