Abstract: A double extruded heat sink for a thermoelectric cooler is disclosed which includes first and second finned plates. The first (base) plate has spaced long fins and pairs of spaced short fins spaced between adjacent long fins. The end fins have male members formed thereon. The second plate has spaced long fins. Each long fin corresponding with the space between the pair of spaced short fins of the first plate for engaging the inner surfaces of the spaced short fins and making good thermal contact therewith when the first and second plates are press fitted together. The end fins of the second plate's fins have female members formed thereon for engaging the male members to lock the first and second plates together when press fitted. The long fins of the first and second plates are serrated to increase their heat dissipating areas. The double extruded heat sink thereby provides a number of fins substantially greater than can be obtained using single extrusion techniques.