Hello Sahrzad! Welcome to Bahrainside!
You did not write where are you from. The answer to your question depends on your nationality.
The official process is the next:
You must send official application in writing to HM The King or to HRH The Prime Minister.
Below are the requirements:
! Nationals of Arab countries should have lived in Bahrain for at least 15 years.
! Nationals of non-Arab countries should have lived in Bahrain for at least 25 years.
* You must be able to read, write and speak Arabic.
* No criminal record.
* Good character, and all the nice things that go with that.
This is the long process .
Another way is residency - the form of 2 year renewable visas.
You can get it as home owner, investor or retiree.