There are two tracks in Seoul National University - SNU International Admissions: International Admissions I and International Admissions II.
International Admissions I:
Both the applicant and his/her parents are not citizens of Korea; the applicant is a high school graduate or has attained an equivalent level of education.
International Admissions II:
The applicant holds either Korean (including international marriage migrants who are naturalized as Koreans) or foreign citizenship and undertook all of his/her education (both primary and secondary; from the first year of elementary school to high school graduation) outside of Korea.
Please note that there is no mentioned percentage/percentile/marks needed that would ensure that you will get admission in SNU. Generally, a percentage of 90% and above is advisable in your board exams.
Along with this, either proof of Korean or English proficiency is required:
1) Korean Proficiency: TOPIK level 3 or higher
2) English Proficiency: TOEFL iBT 80, TEPS 551, IELTS 6.0 or higher
3) Other official documents indicating proof of language proficiency (i.e. SNU Korean Language Center Level 4 or higher)
Application Fee for Undergraduates: 70,000 Won (KRW)
Please visit the below link for further information.