Layered tellurides have been extensively studied as a platform for investigating the Fermi surface (FS) nesting-driven charge density wave (CDW) states. ${\mathrm{EuTe}}_4$, one of the quasi-two-dimensional binary rare-earth tetratelluride CDW compounds with unconventional hysteretic transition, is currently receiving much attention. Here, the CDW modulation vector, momentum, and temperature dependence of CDW gaps in ${\mathrm{EuTe}}_4$ are investigated using angle-resolved photoemission spectroscopy. Our results reveal that (i) a FS nesting vector $\mathit{q}\approx 0.67{\mathit{b}}^{*}$ drives the formation of the CDW state, (ii) a large anisotropic CDW gap is fully open in the whole FS and maintains a considerable size even at 300 K, leading to the appearance of semiconductor properties, (iii) an abnormal behavior of CDW gap in magnitude as a function of temperature, and (iv) an extra, larger gap opens at higher binding energy due to the interaction between the different orbits of the main bands.

• Charge density waves
• Electronic structure
• Nesting
• Semiconductor compounds
• Angle-resolved photoemission spectroscopy