In recent years, there has been a significant effort to investigate the impact of nontrivial electronic topology on the thermoelectric properties of materials. Topological insulators (TIs) and two-dimensional semimetals, in particular, have emerged as an efficient class of thermoelectric materials. When the Fermi level lies within the insulating gap, thermoelectric transport in two-dimensional (2D) topological insulators is primarily determined by the one-dimensional helical states, while in three-dimensional TIs, the transport is driven by the 2D states that exist on the material's surfaces. Here, we review existing results on HgTe quantum wells, which are exemplary in combining the optimal features of topological insulators and the best-performing thermoelectric materials. In addition, we also cover thermoelectric phenomena in two-dimensional semimetals. These materials have overlapping electron and hole bands in the energy space, resulting in a strong mutual friction between them that affects thermoelectric transport and leads to temperature-depend„ent resistivity. Our review focuses on the thermopower phenomena observed in HgTe-based semimetals, taking into account diffusive and phonon drag effects. Furthermore, we also discuss Weyl two-dimensional semimetals with gapless cone spectra and their thermoelectric properties. We highlight the impact of the coexistence of Dirac and heavy holes in the valence band on the thermoelectric properties of the material and their potential for application in thermoelectric devices.