"Add semicolon and goto new line" hotkey

Pressing Ctrl + Shift + Enter twice should do the job. You can record a keyboard macro that does it, and assign a custom shortcut to it.

It's 2020 now and Ctrl + Shift + Enter shortcut now works as expected in Android Studio (tested 4.1.1). MacOS version should have a different modifier, but should be almostly same.

You can customise your shortcuts in preferences - > Keymap

Edit or add new shorts cut is very easy from here.

Another way to get the IDE to add semicolon If you have code completion enabled you can press tab on your code snippet, then press shift+enter to go to a new line.

For example:
1. type sout and press tab.
2. the editor fills in System.out.println($CursorHere);
3. type "foobar" where the cursor appears.
4. press shift enter and you'll be taken to a new line.