Abstract: A fenestrated centrifugal terminator is described for use in an internally circulating fluid bed reactor or conventional riser reactor. It includes a tubular member having a straight vertical tubular portion the lower end of which is adapted for attachment to the upper end of a riser tube. The upper end of the vertical tubular portion merges into a substantially semi-circular inverted U-shaped tubular loop and terminating in a downwardly directing opening. A ramp portion of shallow angle is provided in the vertical tubular portion adjacent the inner face of the loop and terminating at the inlet to the loop to thereby create a venturi. Commencing at the end of the ramp portion is a semi-circular divider wall dividing the tubular loop into a larger upper flow channel and a smaller lower flow channel. This divider wall has a plurality of longitudinally spaced lateral slots through which the gas being separated from the solids is discharged.