The electrical properties of f.e.t.s with submicrometre gates are investigated by means of a 2-dimensional computer model. It is found that the gain-bandwidth product increases with decreasing gate length and reaches a value of 70 GHz for 0.1 μm gates. This improvement is, however, at the expense of open-circuit voltage gain. A practical limit of the gate length for useful devices is found to be about 0.1 μm.