The drawing shows a cooling system for use in a "flip chip packaging" environment where a large scale integrated circuit chip is mounted in an inverted position on a ceramic substrate and presents a flat upwardly facing cooling surface. The system comprises a silicon plate (18) having a plain lower surface which is attached (e.g. by solder) to the upper surface of the inverted chip to be cooled. The upper surface of the plate (18) is formed with a multiplicity of parallel grooves (20) which register with slots (22A) formed through a second plate (22) sealed to the plate (18). A third plate overlying and sealed to the plate (22) has an inlet port (24C) which communicates with the central slot (22A) and outlet passages (24A) which communicate with the end slots (22a). The port (24A) registers with the outlet end of a flexible bellows pipe (28) through which coolant fluid is supplied to the grooves (20) and the outlet ports (248) of the passages (24A) register with the inlet end of an annular duct formed between the bellows pipe (28) and a co-axial encircling second flexible bellows pipe (32) and through which heated coolant fluid is removed from the grooves (20).