No, South Korean law does not allow half‑siblings to marry; any such marriage is void from the start.
Legal basis in the Civil Code
Article 809, Paragraph 1 of the Korean Civil Code states that a marriage cannot be registered if the parties are blood relatives within the eighth degree (8 chon). The law does not differentiate between full and half siblings; both are considered second‑degree relatives (2 chon). Because this falls well inside the prohibited range, the marriage is illegal.
How the "chon" calculation works
In Korean family law, each parent‑child link counts as one degree. A sibling relationship—whether full or half—adds another link, resulting in 2 chon. The prohibition applies up to the eighth degree, covering cousins as distant as third cousins. Therefore, half‑siblings are explicitly barred from marrying.
Consequences of a prohibited marriage
If a couple somehow registers a marriage that violates the consanguinity rule, Article 815 declares the marriage null and void (muyo). It has no legal effect: no inheritance rights, no spousal visa benefits, and no parental rights for any children born of the union.
Recognition of foreign marriages
Article 26 of the Act on Private International Law requires Korean law to apply when at least one party is a Korean citizen. Even if the ceremony occurs abroad, Korea will not recognize the marriage because the public policy prohibition remains in force.
Comparison with other jurisdictions
Many countries also ban half‑sibling marriages, but Korea’s ban extends further, covering relatives up to the eighth degree. Japan and China stop at the third degree, allowing first cousins to marry, while Korea still treats half‑siblings as completely prohibited.
Practical implications for couples
Couples who discover a half‑sibling relationship should seek legal advice promptly. The only viable option is to dissolve the relationship or remain unmarried, as no legal workaround exists within Korean law.