- JFETs can only be operated in the depletion mode whereas MOSFETs can be operated in either depletion or in enhancement mode. In a JFET, if the gate is forward biased, excess- carrier injunction occurs and the gate current is substantial. Thus channel conductance is enhanced to some degree due to excess carriers but the device is never operated with gate forward biased because gate current is undesirable.
- MOSFETs have input impedance much higher than that of JFETs. This is due to negligibly small leakage current.
- JFETs have characteristic curves more flat than those of MOSFETs indicating a higher drain resistance.
- When JFET is operated with a reverse bias on the junction, the gate current IG is larger than it would be in a comparable MOSFET. The current caused by minority carrier extraction across a reverse-biased junction is greater, per unit area, than the leakage current that is supported by the oxide layer in a MOSFET. Thus MOSFET devices are more useful in electrometer applications than are the JFETs.
For the above reasons, and also because MOSFETs are somewhat easier to manufacture, they are more widely used than are the JFETs.