0234 GMT September 22, 2017
The 23-year-old became a priority target for Barcelona this month after it became clear that the Spanish side couldn't get Arsenal's Hector Bellerin, goal.com reported.
Barcelona announced on Thursday that it had reached a deal for Semedo after Barca’s transfer chief flew to Lisbon to negotiate the Portuguese club’s officials down from their steep €50 million valuation.
It is understood the Catalunya club will pay €30 million up front with €5 million bonuses across a five-year contract.
Semedo is new coach Ernesto Valverde's third signing of the transfer window, following the return of Gerard Deulofeu and arrival of young center-back Marlon.
President Josep Maria Bartomeu stated this week that the club hopes to complete "two or three" deals before the window closes next month.
Last season's La Liga runner up has also been linked with Brazilian midfielder Paulinho.
Barcelona faces the first match of the new season on June 22 when Blaugrana plays Juventus in the International Champions Cup, a preseason tournament taking place across the globe.