An apparatus for processing wafers one at a time. The apparatus has a vacuum chamber 1 into which wafers are loaded through a pair of loadlocks 3, 4 which are spaced one above the other. A robot within the vacuum chamber 1 has a pair of gripper arms 22, 29 which are moveable along and rotatable about a vertical axis 23 so as to be moveable between the loadlocks 3, 4 and a wafer processing position. Each of the loadlocks 3, 4 has a vertically moveable portion 8, 26 which is moveable away from the remainder of the loadlock to provide access in a horizontal plane for one of the gripper arms 22, 29.