Two novel host materials based on carbazole derivatives were synthesized with benzo[b]thiophene (B2tCz) or dibenzothiophene (DB2tCz) for use in evaporation-processed blue phosphorescent organic light-emitting diodes. Both host materials exhibited high glass transition temperatures (T_g = 179 °C for B2tCz and T_g = 185 °C for DB2tCz) and triplet energy levels (E_T = 2.84 eV for B2tCz and E_T = 2.93 eV for DB2tCz). Multilayer devices fabricated using B2tCz or DB2tCz as hosts for the phosphorescence emitter, iridium(III)bis[(4,6-di-fluorophenyl)pyridinato-N,C2′]picolinate (FIrpic), showed maximum current efficiencies of 43.3 and 35.6 cd A⁻¹, power efficiencies of 34.0 and 29.4 lm W⁻¹, and external quantum efficiencies of 24.6% and 20.0%, respectively.