I'm invested in SK Hynix via Interactive Brokers but only since last week.
According to their terms:
• Default Withholding Rate: South Korean dividends are initially withheld at 22% at the omnibus account level.
• Tax Treaty Relief at Source: Tax treaty relief at source is generally not available through the omnibus account structure on Interactive Brokers.
• Reclaims: If your country of tax residence has a double taxation treaty with South Korea that offers a lower rate (for instance, 15% or 16.5% depending on your profile), you must pursue any tax refund/reclaim directly with the Korean tax authorities. Interactive Brokers does not provide tax reclaim services.
• Responsibility: You are solely responsible for determining, reporting, and managing your own tax obligations and refund claims.
Personally, I will not be pursuing the difference via the Korean tax authorities because the dividend yield is almost irrelevant at just 0.23% - reclaiming 7% of that could turn out to be a bureaucratic nightmare.
Basically, on an annual basis, I'll be getting a dividend of €23 per €10,000 invested, will get €5.06 withheld and have an opportunity to chase the Korean authorities for a refund of €1.61 per €10,000 invested.