Abstract: A heat sink has a front side on which a plurality of transistors are situated and a back side in which groooves are formed, each groove being directly opposite a transistor. Two-legged clips each have one leg which holds a transistor against the heat sink and another leg that mates with one of the grooves. A ledge is formed on the front side of the heat sink to form a stop for the bottom edge of each transistor, and each groove terminates in a clip-stop ledge for positioning the leg of a clip. Optionally, a plurality of alignment tabs are formed on the ledge to assist in correctly positioning the transistors.