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How fast can modern transistor switches turn on and off?

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NMOS transistorNegative-channel metal-oxide semiconductors (NMOS) employ a positive secondary voltage to switch a shallow layer of p-type semiconductor material below the gate into n-type. For positive-channel metal-oxide semiconductors (PMOS), all these polarities are reversed. NMOS transistors are more expensive, but faster, than PMOS transistors. — transistor NMOS transistor
Negative-channel metal-oxide semiconductors (NMOS) employ a positive secondary voltage to switch a shallow layer of p-type semiconductor material below the gate into n-type. For positive-channel metal-oxide semiconductors (PMOS), all these polarities are reversed. NMOS transistors are more expensive, but faster, than PMOS transistors.

Modern transistors function as high-speed switches that enable the binary operations essential to digital computers and microprocessors. By applying a voltage to the gate electrode, the transistor regulates the flow of current between the source and the drain, effectively toggling the circuit between "on" and "off" states.1

The switching speed of these devices has advanced significantly over time. While early diffused-base transistors developed in the mid-1950s operated at frequencies above 100 megahertz (100 million cycles per second), the potential switching speeds of modern transistors have reached hundreds of gigahertz. This means that contemporary transistors are capable of performing more than 100 billion on-and-off cycles per second.21