A variety of leadless packaging arrangements and methods of packaging integrated circuits in leadless packages are disclosed. The described lead frames are generally arranged such that each device area has a plurality of contacts but no die attach pad. With this arrangement, the back surface of the die is exposed and coplanar with the exposed bottom surface of the contacts. A casing material (typically plastic) holds the contacts and die in place. In one aspect of the invention, the back surface of the die is metallized. The metallization forms a good attachment surface for the package and serves as a good thermal path to transfer heat away from the die. In another aspect, at least some of the contacts have a top surface, a shelf, and a bottom surface. The die is wire bonded (or otherwise electrically connected) to the shelf portions of the contacts. The described package is quite versatile. In some embodiments, the top surfaces of the contacts are also left exposed which provides a very low profile device that is particularly well suited for stacking. A stack of LLP devices can thus readily be provided or other devices can be stacked on top of the described devices. In some embodiments, a heat sink may be attached directly to the metallized bottom surface of the die or package. This tends to provide a good thermal path from the die. In another aspect of the invention, a lead frame panel suitable for use in packaging these semiconductor devices is described.