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 (1, 2) 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 (1, 2) 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 (1, 2) 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 (1, 2) 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).