We demonstrate photogating in a graphene/Si–SiO₂ stack, where vertical motion of photogenerated charge is converted into a corresponding change in graphene channel conductance in real time. Under pulsed illumination, holes accumulate at the Si/SiO₂ interface, creating a surface photovoltage that shifts the flat-band condition and electrostatically suppresses graphene conductance. A dual-readout scheme—simultaneously tracking interfacial charging dynamics and the graphene channel—cleanly separates optical charge injection (cause) from electronic transduction (effect). This separation allows for the direct extraction of practical figures of merit without conventional transfer sweeps, including flat-band shift per pulse, retention time constants, and trap occupancy. Interface kinetics then define two operating regimes: a fast, resettable detector when traps are sparse or rapid, and a trap-assisted analog-memory state when slow traps retain charge between pulses. The mechanism is complementary metal-oxide–semiconductor compatible (CMOS-compatible) and needs no cryogenics or exotic materials. Together, these results outline a compact route to engineer integrating photodetectors, pixel-level memory for adaptive imaging, and neuromorphic optoelectronic elements that couple sensing with in situ computation.