Are you married with kids and alone in Korea?
You can deduct dependents here in Korea from your salary income.
Please visit the below website and review the tax guide there, yes it's in English.
Any questions, please feel free to contact me email@example.com
And also you aliens can calculate your year-end tax by yourself at http://www.nts.go.kr/eng/help/help_53.asp?top_code=H001&sub_code=HS05&ssub_code=HSE3