A method of delivering gas into a rector for epitaxial growth of group III nitrides, comprising delivering into a reactor of at least two reactive gas flows, at least one of which is mixed with a carrier gas, using trimethylaluminum, trimethylindium, trimethylgallium, triethylgallium, and their mixtures as a reactive gas—a source of group III metals, and using ammonia as a reactive gas—a source of nitrogen, wherein the gas flows before injection into a reactor are directed to at least one connected with a reactor mixing chamber for formation of gas mixture, and then gas mixture is delivered into a reactor via flow former shaped for laminar flow conditions promotion, and the walls of mixing chamber and flow former are heated and kept at temperature of 40° C. to 400° C., and the internal volume of the mixing chamber fulfills the conditions:
- V<Q·(Pst/P)·(T/Tst)·1 sec, where
- V is the internal volume of a mixing chamber, cm3;
- Q is the total summed flow rate through a chamber, cm3/s under standard conditions;
- Pst, Tst are standard values of pressure and temperature (P=105 Pa, T=273.15 K);
- P is a pressure in the mixing chamber;
- T is a minimal temperature in the mixing chamber.