If you want work as a foreign intern in Seoul, you will require a D4 visa, which is granted for general training – either scholastic training or professional. A D4 visa allows you to stay in the country for any extended period of time to cover your course of training. As with many other visas, you will need to apply for a D4 visa at least a month before you plan to leave, if not before.
For a D4 visa you may be required to obtain a Korean sponsor, but if you are going to Korea with a valid intern organization this may not be necessary. Also, it is routine to prove that you have more than three million won in your bank account by providing a bank statement at immigration along with your application form. If you are an American you will need to obtain a C-4 visa before arriving in Korea, and then have it converted to a D4.
Please see our section “You want to study” for further information on the D4 visa.