A metal gate, in the context of a lateral Metal-Oxide-Semiconductor MOS stack, is just that--the gate material is made from a metal.

For decades, the industry had moved away from metal as the gate material in the MOS stack due to fabrication complications. A material called Polysilicon (silicon, highly doped with donors or acceptors) was used instead because it can be deposited easily and is tolerant to subsequent manufacturing steps which involve extremely high temperatures (in excess of 900-1000 degrees Celsius), where metal was not. Furthermore, metal has a tendency to disperse into silicon during these Thermal Annealing steps.^{citation needed}

However, Polysilicon doesn't offer the near-zero electrical resistance of metals, and is therefore not ideal for charging and discharging the gate capacitance of the transistor.

Now there is a reverse trend to migrate from silicon gate technology to metal gate technology for nano CMOS.

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