The invention relates to a mass transfer tray of a column with a liquid feed on the tray feed side and a liquid discharge on the opposite tray discharge side, and with multiple profile-shaped channels of a U-shaped cross section that are arranged in the tray between the feed and the discharge, parallel to one another and transversely in relation to the direction of liquid flow, and form between them gas passage slits which are covered over by elongated profile-shaped hoods, which have an inverted U-shaped cross section, wherein the side walls of the channels reach into the hoods, and so the channel side walls are covered over by the hood side walls by a height that is less than the height of the channel side walls and the height of the hood side walls, wherein the liquid flows alternately in opposite directions in the channels, and so in every second channel the liquid flows in one direction and in the channels lying in between the liquid flows in the opposite direction, and wherein the hoods are set higher than the channels in the case of the channels and hoods that are closer to the tray feed side, and consequently the heights over which they cover one another are less than in the case of the channels and hoods that are closer to the tray discharge side.