Abstract: A processing tool bay within a semiconductor fabrication site, including a plurality of semiconductor processing tools for processing wafers being arranged in two opposite rows. An intrabay transport system for transporting wafer carriers around the process tool bay at least in a vertical plane in front of one of said two rows of semiconductor process tools comprises at least one vehicle for receiving and delivering a wafer carrier to and from any one semiconductor process tool of said plurality of semiconductor process tools, and a vehicle guiding mechanism. The vehicle comprises a circular compartment structure including a plurality of compartments for buffering said wafer carrier between receiving it at a first location and delivering it at a second location. Each compartment is arranged for accommodating one wafer carrier. The compartment structure is rotatable around a symmetry axis of itself for an alignment.