Abstract: A substrate processing system having a hot reactor with two load locks and two associated load/unload units, and a related method of operating the system, are disclosed. Substrates are concurrently moved from the reactor into one of two load locks and from the other of the two load locks into the reactor. A bidirectional transfer mechanism is used for the concurrent transfers, such that successive transfers in opposite directions are interleaved. Substrates are heated in the load locks prior to processing in the reactor. The reactor applies processing to substrates, to form processed substrates. Processed substrates are cooled in the load locks after processing in the reactor. Respective load and unload units load substrates into the load locks and unload processed substrates from the load locks. The interleaved concurrent transfers minimize or make zero the idle time of the reactor.