Foreign investors are increasingly focusing on China's 'little giant' companies that supply crucial components for the booming humanoid robotics sector.

The surge of interest in Chinese humanoid robotics has raised a practical question for investors, corporate strategists and supply chain executives: who makes the parts? Reduction gears. Torque sensors. Precision bearings. Industrial software. The further one traces the supply chain, the more often the answer leads to companies that are not household names or well understood by foreign investors. Many carry a designation that deserves closer attention: “little giant”. China began cultivating...