Abstract We found a large thermoelectric figure of merit in the hexagonal phase of 2D selenium and tellurium from first‐principles calculations. The hexagonal phase ( α ) is obtained from three atomic layers truncated along the [001] direction of trigonal Te and Se bulk in the equilibrium structure. We found the α ‐Se structure dynamically stable. The calculated electronic structures of α ‐Se and α ‐Te show interesting semiconductor character for both electronic and optoelectronic applications. Furthermore, the obtained elastic properties show that hexagonal tellurene is a softer material than selenene. The thermoelectric figure of merit for hexagonal 2D phase (∼1.0) is larger than those reported for the tetragonal 2D phase (∼0.75) of selenium and tellurium. Additionally, the computed electrical and phonon transport parameters indicate that selenene and tellurene are promising thermoelectric materials; both offer an alternative to recovering residual heat and transforming it into electricity.