Heterocyclic compounds, synthetic methods for preparing the same, and organic light-emitting display devices comprising the same are described. The subject heterocyclic compounds may comprise an aromatic ring or a heteroaromatic ring fused with a carbazole, dibenzothiophene, or dibenzofurane derivative, the compounds featuring rigid backbone structures with high glass transition temperatures and high melting points. The subject heterocyclic compounds may exhibit high electrical stability, improved charge transport ability, high heat resistance and improved light-emitting properties when used in organic light-emitting devices. Organic light-emitting display devices prepared according to the present invention exhibit lower driving voltages, increased luminescent efficiencies and longer lifetimes.