Free clusters of the layered semiconductor materials of type MS2 (M = Mo, W) are studied using mass and photoelectron spectroscopy and compared to theoretical predictions. In contrast to carbon fullerenes, these clusters prefer planar platelet structures. The dangling bonds at the edges are stabilized by excess S atoms. For WnSm- we find that platelet structures dominate for clusters larger than W10S30, the most stable species are W15S42 and W21S56. These platelets have a metallic character and are chemically inert making them interesting building blocks for future nanoelectronics. (c) 2005 Elsevier B.V. All rights reserved.