HEAT SINK

PROBLEM TO BE SOLVED: To provide a heat sink that implements a small pressure loss of a cooling fluid in a cooling passage and satisfactory cooling performance.SOLUTION: A heat sink 10 is so constructed that a fin unit 20 with a plurality of lugs 24 formed is disposed in a passage 18 for a flow of cooling fluid. The fin unit 20 is so formed that a plurality of lug trains 22 each comprising a plurality of lugs 24 lined in a direction perpendicular to the flow direction of the cooling fluid are arranged in the flow direction of the cooling fluid. The heat sink 10 is formed so as to satisfy predetermined conditional expressions, where a (mm) is a distance between the lug trains 22 of the fin unit 20, L (mm) is a length of the lugs 24 in the flow direction of the cooling fluid, t (mm) is a plate thickness of the fin unit 20, and HM (mm) is a passage height for the cooling fluid relative to a baseplate.