Every time Apple manages to squeeze a few more minutes of battery life out of a new generation of iPhones or make them run a little faster, there’s one company—other than Apple itself—that deserves the lion’s share of the credit: Taiwan Semiconductor Manufacturing Co., which manufactures the chips that act as the brains of Apple’s devices.

That’s true, too, of the blame when Apple falls short of its performance goals for iPhones, which typically make a big leap every two years. At the moment, for example, TSMC is struggling with its latest cutting-edge manufacturing technique, which shrinks the size of transistors on chips to 3 nanometers, a change that will allow Apple to include more powerful, less energy-hungry processors in its devices without dramatically increasing their size, according to two people briefed by TSMC on the project.