2010-11: Gilles Senn appeared in one game with Visp's U17 team in Switzerland; spending most of the season with the club's U15 squad.
2011-12: Senn left Visp to play in the Davos youth club. He played four games for the Davos' U17 team in the Elite Novizen as the club's third goalie behind Andrin Christen and Micha Graf. He dressed in four games for Davos' junior team but did not see any action.
2012-13: Senn split the season between Davos' U20 and U17 teams and represented Switzerland in international competition for the first time, playing for the U17 team. He was 3-4-1 and had a 3.43 goals against in eight regular season Junior A games and in three playoff games was 0-2-1 with a 5.00 goals against. Senn played 21 regular season contests and four playoff games for Davos U17 team in the Elite Novizen. In three games with Switzerland's U17 team he had a 2.41 goals against and .922 save percentage.
2013-14: Senn took over as the starter for Davos U20 team as a 17-year-old and played in two international contests for Switzerland's U18 team. He was 17-15-1 with three shutouts and had a 2.76 goals against in 34 regular season games. Senn and had a 5.00 goals against in three playoff games. He was ranked 12th amongst International goaltenders in Central Scouting's mid-term rankings prior to the 2014 NHL Draft.