We demonstrate the effectiveness of our disruptive controlled spalling technology for making high-efficiency (28.7%) thin-film InGaP/(In)GaAs/Ge tandem solar cells. The controlled spalling technique was employed to separate the thin-film tandem cells (∼14μm) from the host Ge substrates. The electrical characteristics of the thin-film cells (spalled) were examined and compared against the bulk cells (non-spalled) on original Ge wafers. Furthermore, the structural integrity of the transferred thin-film cells was scrutinized using transmission electron microscopy. Our results confirm that the structural properties and the intrinsic material parameters (such as minority carrier lifetime, surface recombination velocity, etc) of the thin-film tandem solar cells are unchanged after spalling.