Fiorentina originally brought Gosens in from Union Berlin in the summer of 2024, initially on loan before making the move permanent.
The 32-year-old expressed his excitement at returning to a club he has supported since childhood.
"Everyone at Schalke 04 worked incredibly hard to get me here. They showed me their plan and explained exactly what my role will be and what they expect from me. It was incredibly convincing. I'm really excited about it. I want to lead by example with my performances and take responsibility," Gosens told the club's website.
He went on to describe the emotional significance of the move.
"Everyone knows I have a special connection to Schalke. I'm really excited about this challenge and really looking forward to getting out on the pitch with the guys and giving absolutely everything I have," he continued.
Schalke, who won promotion back to the Bundesliga after a three-year absence by winning the 2. Bundesliga title last season, view Gosens as far more than a straightforward squad addition given his profile and leadership experience at a higher level than most of his new teammates.
Under head coach Miron Muslic, the club are hoping his experience of European football at Atalanta, Inter and Fiorentina can help steady a squad adjusting to life back in Germany's top flight.
Gosens made his name at Atalanta before moves to Inter Milan and Union Berlin, and his switch to Fiorentina two years ago gave him regular Serie A football. His return to Germany, however, is a full-circle moment on a personal level: Gosens hails from the same wider North Rhine-Westphalia region as Schalke and has long spoken publicly about his boyhood support for the club, having previously come close to joining on at least one occasion earlier in his career before deals fell through.
The loan, with its accompanying purchase option reportedly worth around €1.5m and contingent on the club retaining its Bundesliga status, gives Schalke the chance to assess whether a permanent deal makes sense once the season concludes, while offering Gosens the opportunity to finally play for the club he grew up supporting.