MISFET is a more general term than MOSFET and a synonym to insulated gate field-effect transistor (IGFET). All MOSFETs are MISFETs, but not all MISFETs are MOSFETs. The insulator in a MISFET is a dielectric which can be silicon oxide (in a MOSFET), but other materials can also be employed. The generic term for the dielectric is gate dielectric, since the dielectric lies directly below the gate electrode and above the channel of the MISFET. The term metal is used for the gate material, even though it is usually highly doped polysilicon or some other nonmetal.