Structures and methods for forming the same. A semiconductor chip includes a substrate and a transistor. The chip includes N interconnect layers on the substrate, N being a positive integer. The chip includes a cooling pipes system inside the N interconnect layers. The cooling pipes system does not include any solid or liquid material. Given any first point and any second point in the cooling pipes system, there exists a continuous path which connects the first and second points and which is totally within the cooling pipes system. A first portion of the cooling pipes system overlaps the transistor. A second portion of the cooling pipes system is higher than the substrate and lower than a top interconnect layer. The second portion is in direct physical contact with a surrounding ambient.