It seems trivial to implement it on our own:
implicit def s[F[_]: Monad, A: Semigroup]: Semigroup[F[A]] =
Semigroup.instance((fa, fb) => for {
fa <- fa
fb <- fb
} yield fa |+| fb)
But is it possible to derive it automatically? Kittens seems to work with case classes (at least I tried it for that case and it didn't work).