Apparatus for processing substrate

A substrate processing apparatus that simultaneously forms thin films on a plurality of substrates and performs heat treatment includes: a plurality of substrate holders, each including a substrate support that supports a substrate and a first gas pipe having one or a plurality of injection holes; a boat where the plurality of substrate holders are stacked and including a second gas pipe connected with the first gas pipe of each of the substrate holders; a process chamber providing a space in which the substrates stacked in the boat are processed; a conveying unit that carries the boat into/out of the process chamber; a first heating unit disposed outside the process chamber; and a gas supply unit including a third gas pipe connected with the second gas pipe and supplying a heated or cooled gas into the second gas pipe.