PURPOSE: To increase the yield of a reaction gas, by a method wherein one reaction chamber and the other reaction chamber are connected by a conduit in order to utilize the exhaust gas of the former as at least a part of the reactant gas of the latter.

CONSTITUTION: Silane gas is intrdouced from an introducing valve 22 to form an amorphous silicon layer. Unreacted SiH4 gas is sent to a removing device 35 through a pump 34 through a valve 32 to remove the solid dust therein. In the next step, the gas is sent to gas mixers 14, 15 through a conduit 10 to be mixed with B2H6 introduced from a valve 16 and PH3 introduced from a valve 17 and the resulting mixture is respectively introduced into the first reaction chamber 11 and the third reaction chamber 13 through valves 21, 23 to be used for the formation of a P type amorphous silicon layer and an n type amorphous silicon layer.