Ultrahigh pressure generation at high temperatures is technologically challenging for large sample volumes. In this study, we successfully generated pressures of 37.3–40.4 GPa at 1900–2100 K in a Walker-type large-volume press (LVP). Expansion of the pressure range at high temperatures was achieved by adapting newly designed ZK01F tungsten carbide (WC) anvils with tapered surfaces and using cell assemblies with an ∼1 mm³ sample volume and hard materials, as well as by applying certain adjustments to the apparatus. The pressure efficiencies of the different types of WC anvils and cell assemblies were also studied. Using the above-mentioned techniques, we successfully synthesized and characterized bulk samples of nearly pure sp³-hybridized ultrahard amorphous carbon, core–shell nanocrystals with high Néel temperatures, as well as large-sized single crystals of lower-mantle minerals. The developed LVP techniques presented here could enable the exploration of the chemical and physical properties of novel materials and Earth’s interior.