This paper presents a 1024-channel ROIC for brain massive digital uECoG, which uses liquid-gate GFETs as active sensors. The proposed channel multiplexing technique at the recording array level allows strong reductions of the sensor-to-circuit connectivity, low-cost hybrid integration and low-power operation. A mixed-signal ROIC architecture and CMOS circuit solutions are introduced to compensate for GFET mismatching and for the preamplifier noise figure loss when upscaling the number of recording sites. The 1024-channel 10-bit 5-kHz 36-uW single-chip design is currently being integrated in 0.18-um CMOS technology and post-layout simulation results are reported.