Abstract: The flame ionization detector, which comprises a supply and an ignition device (7) for the combustible gas, a supply for the sample gas, a combustion chamber (4) in which the sample gas is ionized by the flame, and electrodes (8, 1) to which a voltage is applied in order to generate and measure the ion current, is distinguished in that it is constructed as an integrated planar system of at least three parallel platelet-like substrates (1, 2, 3) which are connected to one another and are processed by microsystem technology methods, with a central substrate (1) comprising nozzles (5, 6) for the gases and the ignition device (7) and a recess which forms a part of the combustion chamber (4), is completed by recesses in the neighboring substrates (2, 3) and is essentially closed together with the nozzle region by these substrates (2, 3), and the neighboring substrates (2, 3) comprise supply channels (10, 11) for the gases.