Everyone who works 15+ hours a week for at least one year in Korea is entitled to severance pay, including foreign workers.
Severance = average daily wage × 30 × (days of service ÷ 365). The average daily wage is the total pay for the last 3 months divided by the number of days (about 91).
The employer must pay within 14 days after you leave. Retirement income tax is usually very low.