What is "misfet"

A MISFET is a metal– insulator (electrical)– semiconductor field-effect transistor.

"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 dioxide (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 historically used for the gate material, even though now it is usually highly doped polysilicon or some other nonmetal.