SoftBank said it would buy Boston Dynamics and Tokyo-based Schaft, which design and manufacture robots that simulate human movement. It did not say how much it paid.
of the company rose as much as 7.9 percent after the deal was announced, hitting a 17-year high.
SoftBank Group Chairman Masayoshi Son said that smart robotics were going to be a key driver of the next stage of the information revolution.
Marc Raibert and his team at Boston Dynamics were technology leaders in advanced dynamic robots, he added.
SoftBank is backing the $93 billion Vision Fund, the world's largest private equity fund that seeks to invest in technologies expected to grow significantly in the near future, such as robotics and artificial intelligence. Boston Dynamics and Schaft could eventually be vested with the Vision Fund.
Son is Japan's richest man, and describes the fund as essential for setting up SoftBank for a data "gold rush" which he expects to happen as the global economy becomes increasingly digitized.
Schaft, a University of Tokyo spinoff, develops bipedal robots designed to negotiate uneven terrain.
"Robotics as a field has great potential, and we're happy to see Boston Dynamics and Schaft join the SoftBank team to continue contributing to the next generation of robotics," an Alphabet spokesperson said.