I am trying to find a document that explains pronunciation differences in /E/ and /I/ sounds between UK and US styles. I think US pronunciation has /'sɛmay/ a lot more often than UK /'sɛmi/. Where can I find a document explaining this difference?
Maybe my 3-year residence in England 35 years ago influenced my American accent, but I use both forms of pronouncing "semi". When using it as a spoken abbreviation for "semi-trailer" I say "sem eye". For "semicircle" I say "sem ee". And some other times I say "sem eye circle".
I don't think there is a fixed rule. I think it is highly individualized.
Keep in mind that there is not one US accent, just like there isn't just one UK accent. They're both collections of dialects and accents. So within the US you could have regional accents where some words, like semi, are pronounced similarly to the UK, and vice versa.
If by US accent you mean the New York accent, and by UK you mean BBC English, then the US version - as per wikitionary, at least - is /sɛmaɪ/, and the UK being /'sɛmi/, as you posted
The reason why US English differs from UK English in the ways that it does is constantly disputed. There are theories that US English is actually more similar to the English used at the time of its colonisation, others argue that it adapted due to so many other languages interacting, at the beginning.
I haven't studied it in detail, but the American-British British-American Dictionary does have sections on pronunciation & dialects.
It's just an accent.
For example, some Americans pronounce Italian how I would pronounce eye talian. Also some Americans would pronounce it how I would pronounce Etalian but again these phonetics are strongly based on regional accents.
Most Americans for semi would (in my regional pronunciation) pronounce it sem eye.
When you learn a new language or dialect you have an accent due to many things which can range from the muscles in your mouth and tongue being developed and familiar with moving in a specific way, to learning new words from literature and pronouncing them how you would expect them to sound in your accent.
You can't find anything because you are looking in the wrong place.
OK so... I was hoping to find a real answer here, but apparently not. It's all about "aah well, one does how he wants depending on personal preference, how they were raised, etc..."
That doesn't really satisfy me. Since I was a kid, I've always been told that when I don't know about something related to language, I should better check with authority sources on the matter, aka : Dictionaries.
So that's what I've done : as has been mentioned by TrevorD, most of them do have phonetics about the words they offer definition for.
After checking Merriam Webster, Cambridge and Oxford (which are 3 of the highest authorities on the matter of English Language as far as I know) they all agree about the phonetics of semi and it is sem-EE, NOT sem-AY.
I could be wrong, but it's really looking like the people saying "semAY" are just trying to invent themselves BS reasons to justify their mistake. (or to not acknowledge they've been making one).
I'm happy for anyone to point me to an official and recognized Dictionary where it is explained semi can be pronounced both sem-EE and sem-AY. Haven't found any so far, except in the fantasies of people saying "sem-AY".