This study reports the first experimental observation of ultrafast charge transfer in photo-excited MoS₂/WS₂ heterostructures using photoluminescence mapping and femtosecond pump-probe spectroscopy. The results show that hole transfer from the MoS₂ layer to the WS₂ layer occurs within 50 fs after optical excitation, a remarkably fast rate for van der Waals coupled 2D layers. This ultrafast charge transfer in van der Waals heterostructures can enable novel 2D devices for optoelectronics and light harvesting. Van der Waals heterostructures, composed of atomically thin 2D layers, have emerged as a new class of materials with fascinating new phenomena. MX₂ heterostructures, particularly MoS₂/WS₂, are exciting for optoelectronic and photovoltaic applications due to their optical bandgap in the near-infrared to visible range and strong light-matter interactions. Theory predicts that many stacked MX₂ heterostructures form type-II semiconductor heterojunctions that facilitate efficient electron-hole separation for light detection and harvesting. The MoS₂/WS₂ heterostructure forms a type-II heterojunction with the conduction band minimum in MoS₂ and the valence band maximum in WS₂. This leads to efficient charge transfer with separated electron and holes in two layers upon optical excitation, which can have a dominating effect on both light emission and photovoltaic responses in MoS₂/WS₂ heterostructures. The study addresses two outstanding questions regarding charge transfer processes in MoS₂/WS₂ heterostructures: (1) How do strong electron-electron interactions and excitonic effects affect charge transfer processes? (2) How fast can charge transfer take place between van der Waals-coupled layers? The results show that ultrafast charge transfer takes place very efficiently in MoS₂/WS₂ heterostructures, with holes in the MoS₂ layer separating into the WS₂ layer within 50 fs upon photo-excitation. The study also demonstrates that the observed sub-50 fs hole transfer time is remarkably short, considering the weak van der Waals coupling between the layers. This ultrafast charge transfer rate is attributed to the close proximity of the two heterolayers, allowing electrons or holes to move less than 1 nm vertically for the charge transfer process to happen. The results suggest that MX₂ heterostructures, with their remarkable electrical and optical properties, hold great promise for future optoelectronic and photovoltaic applications.This study reports the first experimental observation of ultrafast charge transfer in photo-excited MoS₂/WS₂ heterostructures using photoluminescence mapping and femtosecond pump-probe spectroscopy. The results show that hole transfer from the MoS₂ layer to the WS₂ layer occurs within 50 fs after optical excitation, a remarkably fast rate for van der Waals coupled 2D layers. This ultrafast charge transfer in van der Waals heterostructures can enable novel 2D devices for optoelectronics and light harvesting. Van der Waals heterostructures, composed of atomically thin 2D layers, have emerged as a new class of materials with fascinating new phenomena. MX₂ heterostructures, particularly MoS₂/WS₂, are exciting for optoelectronic and photovoltaic applications due to their optical bandgap in the near-infrared to visible range and strong light-matter interactions. Theory predicts that many stacked MX₂ heterostructures form type-II semiconductor heterojunctions that facilitate efficient electron-hole separation for light detection and harvesting. The MoS₂/WS₂ heterostructure forms a type-II heterojunction with the conduction band minimum in MoS₂ and the valence band maximum in WS₂. This leads to efficient charge transfer with separated electron and holes in two layers upon optical excitation, which can have a dominating effect on both light emission and photovoltaic responses in MoS₂/WS₂ heterostructures. The study addresses two outstanding questions regarding charge transfer processes in MoS₂/WS₂ heterostructures: (1) How do strong electron-electron interactions and excitonic effects affect charge transfer processes? (2) How fast can charge transfer take place between van der Waals-coupled layers? The results show that ultrafast charge transfer takes place very efficiently in MoS₂/WS₂ heterostructures, with holes in the MoS₂ layer separating into the WS₂ layer within 50 fs upon photo-excitation. The study also demonstrates that the observed sub-50 fs hole transfer time is remarkably short, considering the weak van der Waals coupling between the layers. This ultrafast charge transfer rate is attributed to the close proximity of the two heterolayers, allowing electrons or holes to move less than 1 nm vertically for the charge transfer process to happen. The results suggest that MX₂ heterostructures, with their remarkable electrical and optical properties, hold great promise for future optoelectronic and photovoltaic applications.