Abstract: A door assembly for semiconductor processing equipment used to treat semiconductor substrates, wafers, photomasks, data disks, and other units. The door assembly is mounted to the front wall of a semiconductor processor enclosure having an access opening by means of a pair of guide rods and corresponding sliding bushings connected to the door which encircle the rods to allow movement of the door along the guide rods. A magnetic rodless piston mounted in an actuator bushing block which is magnetically coupled to an actuator bushing block moves the door assembly along the guide rods. The door assembly telescopically moves toward and away from the access opening to allow units to be installed into and removed from the enclosure, and to close the access opening. A window including an expandable seal is secured to an extension piece of the telescoping door assembly to seal between the door assembly and the access opening.