Maxium frequency of operation of MOSFET

What is the maximum frequency of operation for discrete MOSFET? Please mention few. I want depict the cross coupled oscillator on hybrid MIC.

Depends on the MOSFET.

Take a look at the data sheets from Polyfet, they have quite a few variations.

http://www.polyfet.com/tbplt.htm

depends upon what are you using!