A heat transfer device having a heat source for collecting waste heat from a heat-generating system, the heat transfer device having fins in which the shape of the sides of the fins is preferably circular according to the general expression.gamma..rho..gamma..gamma. ##EQU00001## where.gamma. ##EQU00002## h is the heat transfer coefficient between the fin and the surrounding fluid, k is the thermal conductivity of the fin material,.rho..times..times..theta. ##EQU00003## is the heat flow through the fin semi-base per unit depth and .theta..sub.0 is the difference between the temperatures of the heated surface and the surrounding fluid.