This paper investigates the electrical control of neutral and charged excitons in monolayer molybdenum diselenide (MoSe₂), a group VI transition metal dichalcogenide. The authors demonstrate the unambiguous observation and electrostatic tunability of charging effects in positively charged (X⁺), neutral (X⁰), and negatively charged (X⁻) excitons using field effect transistors via photoluminescence. The trion charging energy is found to be large (30 meV) due to strong confinement and heavy effective masses, while the linewidth is narrow (5 meV) at temperatures below 55 K. The spectral contrast is greater than in any known quasi-2D system. The charging energies for X⁺ and X⁻ are nearly identical, implying the same effective mass for electrons and holes. The study highlights the potential of monolayer MoSe₂ as a true 2D semiconductor, opening avenues for investigating phenomena such as exciton condensation and Fermi-edge singularity, as well as for advanced optoelectronic devices.This paper investigates the electrical control of neutral and charged excitons in monolayer molybdenum diselenide (MoSe₂), a group VI transition metal dichalcogenide. The authors demonstrate the unambiguous observation and electrostatic tunability of charging effects in positively charged (X⁺), neutral (X⁰), and negatively charged (X⁻) excitons using field effect transistors via photoluminescence. The trion charging energy is found to be large (30 meV) due to strong confinement and heavy effective masses, while the linewidth is narrow (5 meV) at temperatures below 55 K. The spectral contrast is greater than in any known quasi-2D system. The charging energies for X⁺ and X⁻ are nearly identical, implying the same effective mass for electrons and holes. The study highlights the potential of monolayer MoSe₂ as a true 2D semiconductor, opening avenues for investigating phenomena such as exciton condensation and Fermi-edge singularity, as well as for advanced optoelectronic devices.