Microsoft co-founder and philanthropist Bill Gates backed Warren Buffett's decision to up his stake in Apple, saying it is the most well-positioned tech company when it comes to profits.

"Apple's an amazing company, and the multiple's not gigantic," Gates told CNBC's "Squawk Box" Monday from Omaha, where Berkshire Hathaway held a weekend of events around Saturday's annual meeting. "The top tech companies do have a very strong profit position right now but Apple has the most of all."

On Friday, Buffett, Gates' longtime friend and CEO of Berkshire Hathaway, revealed that his company bought 75 million shares of the tech giant during the first quarter, adding to the 165.3 million shares Berkshire already owned at the end of last year.

"I think Warren has applied great thinking there," said Gates, who is a Berkshire Hathaway board member. "It's not like a tech speculative company where it's still losing money or anything."

Berkshire invested in Apple in 2016 after someone else at the company bought about 10 million shares. Buffett later looked at the stock and bought "considerably more," the billionaire told CNBC in August.

Shares of Apple were slightly higher in premarket trading on Monday. Last week, the stock had its best week since 2011 after Buffett announced Berkshire's additional shares.

Gates was interviewed alongside Buffett and his longtime investing partner and vice chairman, Charlie Munger, who spoke to the tens of thousands attendees on a wide range of topics from their massive stake in Apple to missing out on Alphabet's Google and Amazon to bashing bitcoin as "rat poison."