Provided are crosslinkable semicrystalline polyester plasticizers useful in thermosetting powder coating compositions. The plasticizers of the present invention are preferably comprised of residues of 1,6-hexanediol and 1,12-dodecanedioic acid, and optionally, residues of trifunctional acids or polyols such as trimethylol-propane, glycerol, trimellitic acid, and the like. The thermosetting powder coating compositions also provided by the present invention exhibit markedly superior properties when compared to compositions lacking said plasticizer. Such coatings exhibit better smoothness, less orange peel, better impact strength and flexibility. In the case of the less-reactive crosslinker such as self-blocked isophorone isocyanate (IPDI), the plasticizers greatly improve the reactivity of the composition and reduce the cure requirement.