Okay… after a day of thinking about what CR wrote and after reading all of the comments, I can see where CR did answer the question, but they didn’t answer clearly, in my opinion.
The answer should have been, “Any oil that contains a very small or very large amount of synthetic oil can be called ‘Semi-Synthetic’ because there is no established standard.”
If CR had been more clear with their answer, I would not have been confused.
I feel better now… 
Should this happen again to you, there is a special place for oil-obsessives…www.bobistheoilguy.com where every conceivable nuance of automotive lubrication is discussed ad-nauseum…
Well CR did answer your question with the first word, then they confused you with the rest of their answer, which you apparently still do not understand and that does not apply to the question. But their answer is accurate for a different question.
cont.
At one time it was simple, regular oil was made from crude oil and synthetic oil was made from natural gas. Chemically, they are pretty much the same but the synthetic oil molecules are more consistent in size and shape. Both are chains of carbon surrounded by hydrogen.
cont.
Oil makers began to find ways to refine crude oil into the same consistency as synthetic oil, giving it the same, or nearly the same performance characteristics so the API decided that if it performed like a synthetic, it could be called a synthetic, even if it is 100% crude in origin.
cont.
And that is what CR was referring to with their answer.
"Well CR did answer your question with the first word, then they confused you with the rest of their answer, which you apparently still do not understand and that does not apply to the question. But their answer is accurate for a different question.
Actually, I do understand CR’s explanation of performance standards vs formula. I don’t understand why they thought that information was necessary to include with the answer to the question proposed.
CR did not correctly answer the O.P.'s question.
There are no performance standards for synthetic motor oil. There is no requirement that a motor oil be superior to refined. The only requirement is that accepted “synthetic” processes be used to manufacture.
Superior motor oil can be made with synthetic processes but just because synthetic processes were used doesn’t mean the oil is superior, or even as good as a good refined oil.
It makes no difference how much synthetic is in semi-synthetic motor oil because synthetic is not a superior property.
The important thing with motor oil:
Everything else is really fluff, sort of like drinking tap drinking water vs bottled water. End result is exactly the same, thirst quenched but taste is slightly different.