I can temporarily increase INT from 8 to 18 with Potion of Intellect, is it possible to temporarily increase INT up to 20?

Depends what you are trying to achieve I guess. You have those tech books.

You could choose to invest five points in Therapeutics to learn the Mind Marvel schematic, which temporarily boosts IN (along with WP, PE and CH) by two points each.* Of course, investing just two points to get your IN to 10 would seem the more logical choice.

Why do you need an IN of 20, anyway? The only thing that needs even an IN of 19 is the topmost level of any tech discipline. If your IN is 18 (or less) and you need 100 skill in a tech college (for example) you can just buy one extra tech manual instead.

*To be fair, I've never tried it, so I don't know whether it stacks with a potion of IN.

Thanks TwoHandedSword, you always give great advices mate.

I aimed for 20 temporary INT for a 1 time crafting, which means I need to buy less manuals, but I guess having to buy 1 or 2 more manuals is not such a big deal also.

As always, happy to help. And it's not like those manuals are likely to go to waste, especially if you're playing as a techie.