In a 300 mm IC foundry fab, the intrabay automation systems are more important than a 200 mm one. In general, the intrabay automation systems include the automated controls of the process tools, overhead hoist transports (OHTs) stockers, and rail shortcuts. These control systems are operated concurrently. They must be cooperated seamlessly to increase the system performance and to avoid deadlocks. In this paper, the behaviors of the intrabay automation systems are modeled using the distributed agent oriented Petri net (DAOPN). The fab intrabay DAOPN models are categorized into the new order generation, OHT vehicle dispatching, zone control, path decision, and tool processing models. Finally, the DAOPN is defined, and the models of the intrabay system with one stocker, five tool stations, one OHT loop, and two rail shortcuts are modeled and simulated using the proposed DAOPN. The simulation results are evaluated based upon the conditions of changing the number of OHT vehicles and the dispatching rules.