One.
There should be one space after a semi colon.
There is one space after a semi colon: Example: I went to the store and forgot coffee; potatoes and milk.
One space after a semicolon.
Only one space follows a semicolon.
I was taught it was two. A good way to remember this is by counting the dots on it. The colon has two so it has two spaces. A semi colon has only one dot, and it has only one space after it. But this only applies when the name of the punctuation has the word "colon" in it, as when you are counting the dots in a period, you only see one, but after a period, you usually put two spaces unless you are using a wesite address or something of that sort.
THis is a semi colon ;
You use one space after a colon or semi-colon.
Semi colon looks like this ;
THis is a semi colon ;
In typing, proper style is 2 spaces after a period (.), as well as after a colon (:).
Just one
One.