Substrate processing apparatus including heat-shield plate

Provided is a substrate processing apparatus. The substrate processing apparatus in which processes with respect to substrates are performed includes a lower chamber having an opened upper side, the lower chamber including a passage allowing the substrates to pass therethrough in a side thereof, an external reaction tube closing the opened upper side of the lower chamber to provide a process space in which the processes are performed, an internal reaction tube disposed within the external reaction tube, the internal reaction tube being disposed around a substrate holder placed in the process position to define a reaction region with respect to the substrates, a heater disposed outside the external reaction tube to heat the process space, the substrate holder on which the one or more substrates are vertically stacked, the substrate holder being movable between a stacking position in which the substrates are stacked within the substrate holder and a process position in which the processes with respect to the substrates are performed, and a heat-shield plate disposed under the substrate holder to close an opened lower side of the internal reaction tube when the substrate holder is disposed at the process position.