We establish the topological conditions underlying the thermal stability of C(3)0Si(30) clusters. Two topologies have been considered: a segregated one, where Si and C atoms lie on neighboring and yet, separated parts of the cage, and a non-segregated one, where the number of Si-C bonds is maximized. The segregated network is energetically favored against the non-segregated one, both structures being fully relaxed at T = 0 K. Conversely, the non-segregated structure is the only one stable at finite temperatures, regardless of the nature of the local states (d or p) included in the Kleynman-Bylander construction. (C) 2011 Elsevier B.V. All rights reserved.