The study reports the spectroscopic identification of tightly bound negative trions in monolayer MoS₂, a two-dimensional (2D) atomic crystal. Trions, composed of two electrons and a hole, exhibit a large binding energy of approximately 20 meV, making them significant even at room temperature. This binding energy is significantly larger than that observed in conventional quasi-2D systems, such as semiconductor quantum wells, due to enhanced Coulomb interactions in monolayer MoS₂. The research uses field-effect transistors (FETs) to investigate the optical response of monolayer MoS₂ as a function of carrier density, revealing the presence of both excitons and trions. The trion binding energy is determined to be 18.0 ± 1.5 meV, and the study also demonstrates the unique spin and valley properties of trions, which can be controlled by optical pumping. These findings open new avenues for fundamental studies of many-body interactions and optoelectronic applications in 2D atomic crystals.The study reports the spectroscopic identification of tightly bound negative trions in monolayer MoS₂, a two-dimensional (2D) atomic crystal. Trions, composed of two electrons and a hole, exhibit a large binding energy of approximately 20 meV, making them significant even at room temperature. This binding energy is significantly larger than that observed in conventional quasi-2D systems, such as semiconductor quantum wells, due to enhanced Coulomb interactions in monolayer MoS₂. The research uses field-effect transistors (FETs) to investigate the optical response of monolayer MoS₂ as a function of carrier density, revealing the presence of both excitons and trions. The trion binding energy is determined to be 18.0 ± 1.5 meV, and the study also demonstrates the unique spin and valley properties of trions, which can be controlled by optical pumping. These findings open new avenues for fundamental studies of many-body interactions and optoelectronic applications in 2D atomic crystals.