I have reduced hot water at kithchen tap only! All other taps are OK. WHY?

I'm going to bet a plugged water line -- either in the faucet, the faucet cartridge, or in the pipe, itself.

And I'm going to bet that Perito will win his bet because he covered all bases. However That's not helping is it? First of all, what's the brand name of your faucet?
I can give you a general solution but to get specific I'll need more information.
Shut the water off under the cabinet and open up the valve, remove the cartridge and check and clear the inlet ports. Now, place a pan over the open faucet and turn on, first the hot water. Did you get a strong stream,(let me know) and then the cold. This flushes out the supplies. If you need more explainations I'll need to know all the details you can furnish me. Good luck, Tom