The Un Certain Regard is one of the two parts of the official competition programme of the Cannes Film Festival, dedicated to discovering new directorial poetics and aesthetics, HAVC said.
The prize is the most important mark of recognition so far for Matanic and producer Ankica Juric Tilic, who has worked on a number of his films.
This year's Cannes Film Festival jury was presided over by Italian actress Isabella Rossellini.
Around 20 films competed in the "Un Certain Regard" section.
The High Sun is the first Croatian film to enter the Cannes Film Festival's official selection. It is a Romeo and Juliet-based love story about two people from different ethnic groups.
The film was co-produced by the Zagreb-based Kinorama, the Slovenian film company Gustav Film and SEE Film Pro from Serbia.