The 23-year-old joins the Cherries from Championship outfit Bristol City, where he had spent the last six years.
Semenyo made a great start to the 2022/23 campaign after registering three goals in four appearances in the Championship.
His form has impressed Bournemouth, who have decided to spend £9 million to bring him to Dean Court.
A statement from the Premier League club said. “AFC Bournemouth have completed the signing of Ghanaian international Antoine Semenyo from Bristol City.
“The forward joins on a four-and-a-half-year deal, with the club retaining an option of a further year.”
Meanwhile, Bournemouth chief executive Neill Blake added: "Antoine is an exciting player and one we have monitored for a while.
"He had interest from elsewhere and so we're delighted to welcome him to the club."
Semenyo has played six times for Ghana and scored one goal. He was also part of the Black Stars side that featured at the Qatar 2022 World Cup.