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 (7, 82) 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 (21, 22, 23) is present, wherein the silicon nitride flow tube (21, 22, 23) comprises the combustion chamber (7, 82), wherein the combustion chamber (7, 82) is thermally insulated within the opening of the system chip, forming an island on which the combustion chamber (7, 82) is situated, which silicon nitride flow tube (21, 22, 23) has two ends, one end with a first channel for supplying the fuel from the fuel inlet to the combustion chamber (7, 82) and a second channel for supplying the gas from the gas inlet to the combustion chamber (7, 82), 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 (7, 82) 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 (21, 22, 23) is present, wherein the silicon nitride flow tube (21, 22, 23) comprises the combustion chamber (7, 82), wherein the combustion chamber (7, 82) is thermally insulated within the opening of the system chip, forming an island on which the combustion chamber (7, 82) is situated, which silicon nitride flow tube (21, 22, 23) has two ends, one end with a first channel for supplying the fuel from the fuel inlet to the combustion chamber (7, 82) and a second channel for supplying the gas from the gas inlet to the combustion chamber (7, 82), 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.