At high temperatures a leakage current flows to the gate of a junction-FET and to the substrate of an MOS-FET. It is shown that in a junction-FET there is shot noise of the gate current and a strongly correlated noise component in the drain current. In an MOS-FET the effect of the leakage current is less significant, but there is a shot noise component at the drain. Leakage currents seriously effect the low-noise operation of junction-FET's whereas the effect in MOS-FET's is relatively small. © 1969.