It would probably be intended to include the 17th, but there is some doubt - so it's common to write
The first semester classes will be from 1st September until 17th January (inclusive)
to be absolutely clear that there are classes on both 1st September and 17th January.
You can write
The first semester classes will be from 1st September until 17th January (exclusive)
If there are no classes on the first and last dates listed, but I don't know of an easy way to include one date but not the other without adding more words.