This study reports the atomic-level polarization reversal in sliding ferroelectric semiconductors, specifically in van der Waals (vdW)-layered yttrium-doped γ-InSe. The research directly observes real-time interlayer sliding along the armchair direction, corresponding to vertical polarization reversal. The sliding is driven by low-energy electron-beam illumination, suggesting low switching barriers. A new sliding mechanism is proposed, where two bilayer units slide towards each other simultaneously, supporting the observed reversal pathway. The findings provide important insights into polarization reversal via atomic-scale interlayer sliding, advancing research on sliding ferroelectrics for non-volatile storage and ferroelectric field-effect transistors. The study highlights the role of yttrium doping in enhancing ferroelectricity in γ-InSe by reducing stacking faults and increasing polarization. First-principles calculations show that Y-doping lowers the sliding barrier and stabilizes the crystal structure. The research also demonstrates that the interlayer sliding induces multiple polarization states, which are crucial for neuro-inspired computing applications. The results confirm the existence of multi-level polarization states in this material system, offering promising applications for slidetronics in ultrathin layers and semiconductors with high-speed data processing under low energy cost. The study also reveals the role of Y-doping in optimizing sliding barriers and increasing OOP polarization, leading to robust ferroelectricity in InSe:Y. The findings contribute to the understanding of sliding ferroelectricity in 2D materials and its potential applications in next-generation electronic devices.This study reports the atomic-level polarization reversal in sliding ferroelectric semiconductors, specifically in van der Waals (vdW)-layered yttrium-doped γ-InSe. The research directly observes real-time interlayer sliding along the armchair direction, corresponding to vertical polarization reversal. The sliding is driven by low-energy electron-beam illumination, suggesting low switching barriers. A new sliding mechanism is proposed, where two bilayer units slide towards each other simultaneously, supporting the observed reversal pathway. The findings provide important insights into polarization reversal via atomic-scale interlayer sliding, advancing research on sliding ferroelectrics for non-volatile storage and ferroelectric field-effect transistors. The study highlights the role of yttrium doping in enhancing ferroelectricity in γ-InSe by reducing stacking faults and increasing polarization. First-principles calculations show that Y-doping lowers the sliding barrier and stabilizes the crystal structure. The research also demonstrates that the interlayer sliding induces multiple polarization states, which are crucial for neuro-inspired computing applications. The results confirm the existence of multi-level polarization states in this material system, offering promising applications for slidetronics in ultrathin layers and semiconductors with high-speed data processing under low energy cost. The study also reveals the role of Y-doping in optimizing sliding barriers and increasing OOP polarization, leading to robust ferroelectricity in InSe:Y. The findings contribute to the understanding of sliding ferroelectricity in 2D materials and its potential applications in next-generation electronic devices.