Semih Kılıçsoy was born on August 15, 2005, in the Gaziosmanpaşa district of Istanbul. He began playing football in 2014 with GOP Venüs. He later spent a brief period at Arnavutköy Yaylaspor. In 2016, he joined the Beşiktaş youth academy and competed in various age categories. He attracted attention by scoring 33 goals for the Beşiktaş U14 team.

After a long development period within the Beşiktaş youth system, Kılıçsoy recorded 42 goals in 64 matches in the U19 Super League. He signed his first professional contract on October 21, 2021. He made his debut with the senior team in the 2022–23 season. In the 2023–24 season, he scored 10 goals in the Super League, becoming the second youngest player in club history to reach this milestone in a single season. In 2023, by scoring against Tirana, he became the youngest player to score for Beşiktaş in European competitions.

Semih Kılıçsoy has represented Türkie at various youth national team levels, progressing from the U14 level to the senior national team. He made direct contributions to 30 goals in 35 matches across youth and senior levels. In 2024, he received his first call-up to the senior national team and was included in the squad for the European Championship the same year.

Kılıçsoy primarily played as a centre-forward. He also played on both wings and occasionally in the attacking midfield position.

• U19 Elite A League Top Scorer in the 2022–23 season: 18 goals in 17 matches
• Youngest player to score in European competitions for Beşiktaş
• Youngest player in Süper Lig history to score in four consecutive matches
• The second youngest player in Beşiktaş history to score 10 goals in a single season

Semih Kılıçsoy signed a professional contract with Beşiktaş on May 5, 2023. On January 11, 2024, his contract was extended until June 30, 2028.