A light-emitting device including a heterocyclic compound, an electronic apparatus including the light-emitting device, and the heterocyclic compound are provided. The light-emitting device also includes a first electrode, a second electrode facing the first electrode, and an interlayer between the two electrodes and including an emission layer. The triplet energy level and glass transition temperature of the heterocyclic compound are configured such that the luminescence efficiency and lifespan of the light-emitting device may be enhanced or improved.