This study investigates the exciton binding energy and excited states in monolayer tungsten diselenide (WSe₂) using combined linear absorption and two-photon photoluminescence excitation spectroscopy. The exciton binding energy is determined to be 0.37 eV, which is significantly larger than that in III-V semiconductor quantum wells, making the exciton excited states observable even at room temperature. The exciton excitation spectrum, which includes both one- and two-photon active states, is distinct from the simple two-dimensional (2D) hydrogenic model. This result indicates significantly reduced and nonlocal dielectric screening of Coulomb interactions in 2D semiconductors. The large exciton binding energy has significant implications for next-generation photonics and optoelectronics based on 2D atomic crystals. The study reveals that the exciton binding energy in monolayer WSe₂ is about 0.37 eV, with a band gap energy of 2.02 eV. The observed exciton states show a more even spacing compared to the simple 2D hydrogenic model, indicating nonlocal dielectric screening effects. The results are distinct from the predictions of the simple 2D hydrogenic model, which ignores screening. The study also demonstrates that the exciton binding energy can be determined through experimental measurements without relying on specific exciton models. The findings highlight the importance of Coulomb interactions and excitonic effects in 2D semiconductors, and provide new opportunities for studying and controlling spin/valley polarization in 2D transition metal dichalcogenides. The results are significant for future optoelectronic devices based on 2D semiconductors.This study investigates the exciton binding energy and excited states in monolayer tungsten diselenide (WSe₂) using combined linear absorption and two-photon photoluminescence excitation spectroscopy. The exciton binding energy is determined to be 0.37 eV, which is significantly larger than that in III-V semiconductor quantum wells, making the exciton excited states observable even at room temperature. The exciton excitation spectrum, which includes both one- and two-photon active states, is distinct from the simple two-dimensional (2D) hydrogenic model. This result indicates significantly reduced and nonlocal dielectric screening of Coulomb interactions in 2D semiconductors. The large exciton binding energy has significant implications for next-generation photonics and optoelectronics based on 2D atomic crystals. The study reveals that the exciton binding energy in monolayer WSe₂ is about 0.37 eV, with a band gap energy of 2.02 eV. The observed exciton states show a more even spacing compared to the simple 2D hydrogenic model, indicating nonlocal dielectric screening effects. The results are distinct from the predictions of the simple 2D hydrogenic model, which ignores screening. The study also demonstrates that the exciton binding energy can be determined through experimental measurements without relying on specific exciton models. The findings highlight the importance of Coulomb interactions and excitonic effects in 2D semiconductors, and provide new opportunities for studying and controlling spin/valley polarization in 2D transition metal dichalcogenides. The results are significant for future optoelectronic devices based on 2D semiconductors.