At a time when investor attention has been on the semiconductor industry, some hidden gems with businesses quite dissimilar to high tech have turned out to be market winners, riding the AI boom. Toto is best known for high-end toilets, Nittobo makes textiles and glass fiber, and Ajinomoto makes MSG seasoning. Their shares have gained 78%, 63% and 61%, respectively, this year, as they make use of their core technologies to benefit from the AI supply chain.

Toto makes ceramic electrostatic chucks used in semiconductor manufacturing equipment, while Nittobo supplies advanced glass fiber used in semiconductor package substrates. Ajinomoto makes insulating material, known as "build-up film" or ABF, used in semiconductor packaging for high-performance computers and data-center servers. All three companies reported sharp growth in businesses tied to semiconductor demand for their full financial years ended March 31, highlighting the impact of the AI boom.

Toto: plugging away The company's advanced ceramics business enjoyed higher profit margin than its housing equipment segment, thanks to demand from IoT, digital transformation, AI and data centers for advanced semiconductor equipment. Toto, in its full year results, said it saw a decrease in sales and profits for its core 100-year-old housing equipment unit, but this was made up by increases in revenue and profits in its advanced ceramics business. The segment saw a 34% increase in annual revenue and 42% jump in operating profit, almost single-handedly pulling the overall company into growth for the financial year.

The company's expertise in ceramics led it to manufacture electronic chucks for semiconductor manufacturing equipment in 1988. These chucks hold silicon wafers in place during the etching process inside semiconductor manufacturing equipment. Toto says that their ceramics significantly contribute to improving the manufacturing yield of advanced chips.

"However, we do not view one segment as superior to the other. Our Advanced Ceramics Business is a high-growth area, but we endured long periods of deficits over its 40-year history before reaching this point," the company said to CNBC in an email. It plans to grow both segments and "maintain a balanced ratio" for sustainable overall growth, and "absolutely no plans" to pivot away from its core housing equipment business, as it provides a stable foundation for the company's balance sheet, while the chip sector remains volatile.

Nittobo: looking to ride the boom Nittobo said electronic materials were already its mainstay, as it continues to develop markets for its traditional glass-fiber business. Its T-glass product, launched in 1984, is used in printed circuit boards, and electronic components. The company told CNBC that its T-glass and other electronic materials are "the pillar" of its growth for the next decade, and that AI semiconductor demand was changing how it allocates capital expenditure, research and development, and human resources.

Nittobo's results tell the story: the company said that strong demand related to AI servers, as well as factors such as strong sales of "Special Glass" pushed up sales and profits for the electronics materials business segment.