Can I put high gloss polyurethane right over semi gloss?

...which was just???????? the answer is in general yes, but unless the gloss is less than 4 hours old, it will need a light sanding to scratch the surface so the next coat will bond. However, if you're not happy with the gloss because of shine, try rubbing it down with 4 ought (0000) steel wool, available at any hardware or big box home store. this will knock down the shine without scratching the surface. This is not the same as sanding, if thats your plan, to do another coat, you'll need to light sand the gloss before applying the next coat.

In order for the right answer you need to finish your question.

Best to sand it a bit so it sticks well, and cause high-gloss will show every bump, pit and brush stroke. I apply is with a smooth 6" roller, and then very finely use a real good badger brush to feather it to get rid of any texture from the roller.

Sand first and then you shouldn't have a problem- good luck!

There is no need to sand unless there are surface flaws. All you need to do is give it a good cleaning and rinse, and then a scuff sand with something like a scotch bright pad.

This comment is coming from a retired old school painting contractor.