  The supersymmetric p-branes of Type II string theory can be interpreted after
compactification as extremal black holes with zero entropy and infinite
temperature. We show how the p-branes avoid this apparent, catastrophic
instability by developing an infinite mass gap. Equivalently, these black holes
behave like elementary particles: they are dressed by effective potentials that
prevent absorption of impinging particles. In contrast, configurations with 2,
3, and 4 intersecting branes and their nonextremal extensions, behave
increasingly like conventional black holes. These results extend and clarify
earlier work by Holzhey and Wilczek in the context of four dimensional dilaton
gravity.
