In an electrical component package provided with a liquid-cooled heat exchanger, a main-body plate of the package and a crowning member that are composed of metal plates are joined together, forming a hollow part therebetween for use as a liquid-cooled heat exchanger in which a working fluid is sealed. A concavity for use in mounting an electrical component to be cooled is formed on the outer surface portion of the main-body plate of the package disposed opposite to the hollow part. An inner surface portion that faces into the hollow part of the main-body plate of the package is carved out using a carving tool, whereby fins are formed at a fine pitch on the inner surface portion. Minute channels for moving the working fluid are formed between the fins. Therefore, a flat electrical component package can be provided with a liquid-cooled heat exchanger that has excellent heat-radiating functionality.