Wikipedia has a great source of info on
public holidays in South Korea.
As a general guideline (dates do vary slightly with the lunar calendar each year):
- January 1~2: New Year's Day
- January 22~24: Lunar New Year
- 1 week in late February: Spring vacation (for junior and high school)
- March 1: Independence Movement Day
- April 5: Arbor Day
- May 5: Children's Day
- May 8: Fathers and Mothers' Day
- May 28: Buddha's Birthday ("Feast of the Lanterns Day")*
- June 6: Memorial Day
- Mid-July~mid-August: Summer vacation
- July 17: Constitution Day
- August 15: Liberation Day
- Late August: School begins
- September 29~October 1: Ch'usok ("Korean Thanksgiving Day")
- October 3: National Foundation Day
- Mid-December~end of January: Winter vacation (for junior and high school)
- December 25: Christmas
The law in Korea states that public holidays don't need to be paid, however most schools are kind enough to pay it.
Best to consult your contract as the dates of holidays are usually found within.