A device for determining the combustion value of a fuel, the device comprising: - a fuel inlet with an intake opening for supplying the fuel to be measured to the device ; - a gas inlet with an intake opening for supplying an oxygen-containing gas to the device ; - a combustion unit connected to the fuel inlet and the gas inlet , which combustion unit is provided with a combustion chamber for chemically reacting the fuel to be measured with the oxygen containing gas in a combustion reaction therein; - a gas outlet connected to the combustion chamber for discharging waste gases produced in the combustion reaction; as well as - means for measuring at least a measure of the amount of energy released by the combustion; - a flow measurement unit disposed between the intake opening of the fuel inlet and the combustion chamber ; - characterized in that the device comprises a system chip with a silicon substrate provided on a carrier , wherein the system chip is provided with the combustion unit , the fuel inlet , the gas inlet and the gas outlet ; - wherein the system chip is provided with an opening within which a silicon nitride flow tube is present, wherein the silicon nitride flow tube comprises the combustion chamber , wherein the combustion chamber is thermally insulated within the opening of the system chip , forming an island on which the combustion chamber is situated, which silicon nitride flow tube has two ends, one end with a first channel for supplying the fuel from the fuel inlet to the combustion chamber and a second channel for supplying the gas from the gas inlet to the combustion chamber , and one end with a downstream channel to discharge flue gas to the gas outlet , where both ends of the silicon nitride flow tube merge into a silicon nitride-coated channel in the silicon substrate via a wall of the opening. - a fuel inlet with an intake opening for supplying the fuel to be measured to the device ; - a gas inlet with an intake opening for supplying an oxygen-containing gas to the device ; - a combustion unit connected to the fuel inlet and the gas inlet , which combustion unit is provided with a combustion chamber for chemically reacting the fuel to be measured with the oxygen containing gas in a combustion reaction therein; - a gas outlet connected to the combustion chamber for discharging waste gases produced in the combustion reaction; as well as - means for measuring at least a measure of the amount of energy released by the combustion; - a flow measurement unit disposed between the intake opening of the fuel inlet and the combustion chamber ; - characterized in that the device comprises a system chip with a silicon substrate provided on a carrier , wherein the system chip is provided with the combustion unit , the fuel inlet , the gas inlet and the gas outlet ; - wherein the system chip is provided with an opening within which a silicon nitride flow tube is present, wherein the silicon nitride flow tube comprises the combustion chamber , wherein the combustion chamber is thermally insulated within the opening of the system chip , forming an island on which the combustion chamber is situated, which silicon nitride flow tube has two ends, one end with a first channel for supplying the fuel from the fuel inlet to the combustion chamber and a second channel for supplying the gas from the gas inlet to the combustion chamber , and one end with a downstream channel to discharge flue gas to the gas outlet , where both ends of the silicon nitride flow tube merge into a silicon nitride-coated channel in the silicon substrate via a wall of the opening. <EOS>