A method of delivering gas into a reactor for multi-layered epitaxial growth of group III nitrides, comprising the steps of: (i) providing a reactor including a device comprising at least two inlets for reactive gas supply and a system for gas injection into the reactor, wherein the system for gas injection into the reactor comprises at least one mixing chamber for formation of a gas mixture and a flow former allowing gas injection into the reactor under the conditions of a laminar flow and connecting the mixing chamber with a reactor inlet , wherein the mixing chamber and flow former further comprise tools for keeping a given temperature, and (ii) delivering into the reactor of at least two reactive gas flows, at least one of which is mixed with a carrier gas, wherein the gas flows before injection into the reactor are directed to the mixing chamber via the at least two inlets and mixed within the mixing chamber , and wherein the walls of the mixing chamber and a connection zone between the mixing chamber and the reactor are preliminary heated up to a temperature of 40°C to 400°C, and the gas mixture is then supplied into the reactor under conditions of laminar flow, wherein trimethylaluminum, trimethylindium, trimethylgallium, triethylgallium, and their mixtures are used as a reactive gas and a source of group III metals, and ammonia is used as a reactive gas and a source of nitrogen, and wherein an internal volume of each mixing chamber fulfills the conditions: V < Q · P st /P · T/T st · 1 sec , wherein V is the internal volume of the mixing chamber in cm 3 ; Q is the total summed flow rate through the mixing chamber in cm 3 /s under standard conditions; P is the maximum pressure in the mixing chamber ; T is a minimal temperature in the mixing chamber ; and P st /T st are standard values of pressure and temperature (P = 10 5 Pa, T=273,15 K). (i) providing a reactor including a device comprising at least two inlets for reactive gas supply and a system for gas injection into the reactor, wherein the system for gas injection into the reactor comprises at least one mixing chamber for formation of a gas mixture and a flow former allowing gas injection into the reactor under the conditions of a laminar flow and connecting the mixing chamber with a reactor inlet , wherein the mixing chamber and flow former further comprise tools for keeping a given temperature, and (ii) delivering into the reactor of at least two reactive gas flows, at least one of which is mixed with a carrier gas, wherein the gas flows before injection into the reactor are directed to the mixing chamber via the at least two inlets and mixed within the mixing chamber , and wherein the walls of the mixing chamber and a connection zone between the mixing chamber and the reactor are preliminary heated up to a temperature of 40°C to 400°C, and the gas mixture is then supplied into the reactor under conditions of laminar flow, Q is the total summed flow rate through the mixing chamber in cm 3 /s under standard conditions; P is the maximum pressure in the mixing chamber ; T is a minimal temperature in the mixing chamber ; and P st /T st are standard values of pressure and temperature (P = 10 5 Pa, T=273,15 K). <EOS>