Emma, the info I have been given is that tax is paid at a rate of 20.9% of the gross income earned (a rate of 26.42% of the NET income). You are supplied with a tax certificate which (assuming your country of residence has a dual taxation agreement with South Korea) may be used to offset tax payments in your country of residence, where you would pay the balance if any.
As a rough guide comparing the tax on the gross income to the tax and National Insurance rates for example in the UK I think you would still be left with a tax liability in the UK of something like 27,000 sterling a year.
Can anybody enlighten me or confirm my thinking is correct?