Upvote:5
No visa is required for a French citizen when entering South Korea. French citizens are allowed to stay up to 90 days visa free in South Korea. Also, 3 hours for transit is plenty of time in any major international airport. So, you will be fine.
The Wikipedia reference describes the visa policy for French citizens.
Also, KLM's TIMATIC Visa Information, used by airlines to confirm passenger requirements, has the same information that no transit visa is required for French nationals for transiting South Korea.
National France (FR)
Embarkation Cambodia (KH)
Transit Korea (Rep.) (KR)
Destination France (FR)
ALSO CHECK DESTINATION INFORMATION BELOWKorea (Rep.) (KR)
VISA NOT REQUIRED.