Field-effect transistors use multi-carrier conduction (multi-carrier: electrons are the majority carriers, referred to as multi-carriers), while transistors use both multi-carriers and minority carriers (holes are minority carriers, referred to as minority carriers). FET is a voltage-controlled device, and its gate basically takes no current, while the base of transistor always takes a certain current. Therefore, when the signal source only allows a small current, FET should be selected. Under the condition of allowing a certain current, a higher voltage amplification factor can be obtained by selecting transistors for amplification.