Tech money proves to be hard-earned as well: All nine of the richest billionaires are self-made, thanks to the powerful companies they built themselves, including Amazon, Facebook, Microsoft, and Google.

For the ranking, Business Insider culled data from the Bloomberg Billionaires Index as of July 27, as well as live data from Amazon’s share price. The index updates daily to provide up-to-the-minute data on the world’s wealthiest men and women. You can read the full methodology here.

Below, read on to see the nine richest billionaires who made their fortunes in tech.

Emmie Martin contributed reporting to an earlier version of this article.

9. Steve Ballmer

Net worth: US$30.6 billion

Age: 61

Country: US

Industry: Technology

Source of wealth: Self-made; Microsoft

Steve Ballmer dropped out of business school at Stanford in 1980 to join Harvard friend Bill Gates at Microsoft as the company’s first business manager, earning a US$50,000 salary and a stake in the company. During his tenure, Ballmer held positions as vice president of marketing, vice president of systems software, and executive vice president of sales and support, and was often referred to as “the numbers guy.”

He became CEO of the company in 2000 after Gates stepped down, and he remained in charge of the software giant until Satya Nadella replaced him in 2014. While running Microsoft, the company’s revenue grew by 294% and profits by 181% — although its market share was surpassed by Google and Apple during the same period. Still, the early stake Ballmer acquired in the company made him immensely wealthy.

After stepping down as CEO, Ballmer fulfilled his dream of owning an NBA franchise, paying US$2 billion in a deal to buy the Los Angeles Clippers, now his main venture.

Ballmer’s net worth has increased US$4.18 billion in the last year.

8. Ma Huateng

Net worth: US$31.1 billion

Age: 45

Country: China

Industry: Technology

Source of wealth: Self-made; Tencent Holdings

Software engineer Ma Huateng (aka Pony Ma) founded China’s largest internet portal, Tencent Holdings, in 1998. He was 26. Ma’s company has a number of successful and widely used platforms in its portfolio, including QQ, its instant-messaging service, which is one of the world’s 10 largest websites; a mobile-texting service (WeChat) with over 900 million users; a mobile-commerce product (WeChat Wallet); and an online-gaming community (Tencent Games), the largest in China.

Ma’s wealth has increased by US$10.3 billion in the past year.

7. Jack Ma

Net worth: US$43.8 billion

Age: 52

Country: China

Industry: Technology

Source of wealth: Self-made; Alibaba

Post-IPO, however, Alibaba’s good fortune began to slip. The company’s shares dropped 22% in 2015, most likely because of China’s slowing economy and concerns over counterfeiters using the company’s platform. Ma didn’t worry, though. He acknowledged that 2016 would be a trying time for the Chinese economy, but remained confident in Alibaba’s long-term success.

Ma’s wealth has increased by US$10.5 billion over the past year.

Alibaba owns South China Morning Post.

6. Sergey Brin

Net worth: US$46.8 billion

Age: 43

Country: US

Industry: Technology

Source of wealth: Self-made; Google

Along with cofounder Larry Page, Sergey Brin helped facilitate Google’s massive restructuring, which the company announced in 2015. The move put Google under the auspices of a holding company called Alphabet, run by Brin as president and Page as CEO. Google’s other ventures, such as Nest and Google X, are separate companies also under the Alphabet umbrella.

The restructuring allowed Brin to focus on exploring inventive new “moonshot” projects and ideas. With top talent and an abundance of resources at its disposal, Alphabet has already started making automated homes and self-driving cars a reality.

Brin, who emigrated from Moscow to the US as a child, connected with Page in 1995 at Stanford, where they were each pursuing a PhD. Three years later they founded Google, now one of the most powerful companies on the planet.

Over the past year, Brin’s wealth has increased by US$7.62 billion.

5. Larry Page

Net worth: US$48.0 billion

Age: 44

Country: US

Industry: Technology

Source of wealth: Self-made; Google

As a Stanford PhD student in 1998, Larry Page teamed up with classmate Sergey Brin to create BackRub, an early search engine. The project eventually morphed into Google — now called Alphabet — one of the largest and farthest-reaching companies in the world, worth more than US$660 billion. Over the past year, Page’s personal net worth has increased by US$8.05 billion.

Page oversaw major changes to Google’s business structure in 2015, starting with the creation of Alphabet, the holding company that manages Google and all of its related ventures, including Nest, Calico, and Google X. Previously the chief executive of Google, Page moved up to helm Alphabet, which has its hand in everything from home automation to self-driving cars to prolonging human life.

Page doesn’t make a lot of splashy purchases, but the alternative-energy advocate does own a yacht and an eco-friendly mansion in Palo Alto that uses geothermal energy and rainwater capture. He’s also an avid kiteboarder.

4. Larry Ellison

Net worth: US$52.9 billion

Age: 72

Country: US

I ndustry: Technology

Source of wealth: Self-made; Oracle

In 1977, Larry Ellison teamed up with two colleagues from an electronics company to start their own programming firm, which landed a contract not long after to build a relational database-management system for the CIA under the project code Oracle. The project grew into what is known today as Oracle Corp., which produced US$37 billion in revenue last year. In 2010, Ellison reduced his annual salary from US$1 million to US$1, but he still takes in more than US$60 million in total compensation thanks to generous stock awards. Ellison stepped down as CEO in 2014 after 38 years on the job and took on the role of chief technology officer.

The tech tycoon is also a generous philanthropist through partnerships with wildlife conservation groups and the Lawrence Ellison Foundation, which supports organizations that research aging and global infectious diseases. He’s also a member of Bill Gates and Warren Buffett’s Giving Pledge, committing to give away at least half of his fortune.

3. Mark Zuckerberg

Net worth: US$70.5 billion

Age: 33

Country: US

Industry: Technology

Source of wealth: Self-made; Facebook

In 2004, Mark Zuckerberg, then a 19-year-old sophomore at Harvard, launched TheFacebook.com, a rudimentary version of the now ubiquitous social network known as Facebook. Zuckerberg dropped out of college to work full-time as Facebook’s CEO, and the site quickly exploded in popularity. Today, it attracts two billion daily users and is worth US$480 billion. At 33, Zuckerberg is by far the youngest of the 50 richest people in the world. His wealth has increased by US$20.5 billion in the past year.

In December 2015, Zuckerberg and his wife, Priscilla Chan pledged give away 99% of their wealth in their lifetimes through an organization called the Chan Zuckerberg Initiative, though some critics noted the organisation wasn’t a nonprofit charity itself and found the announcement misleading.

But this isn’t the couple’s first foray into philanthropy. They donated US$25 million in the fight against Ebola in 2015, and they gave US$100 million worth of Facebook shares toward improving the Newark public-school system.

1. Bill Gates

Net worth: US$90.7 billion

Age: 61

Country: US

Industry: Technology

Source of wealth: Self-made; Microsoft

At just 20 years old, Bill Gates cofounded Microsoft with his childhood friend Paul Allen. Just months before his 31st birthday, the company went public, making Gates a billionaire. He served as CEO of the software titan until 2000 and was its chairman and largest shareholder until 2014. Though he still sits on the company’s board, Gates is no longer actively involved in Microsoft.

Gates held the title of the richest man in the world between May 2013 and July 2017, when he was overtaken by Jeff Bezos on the list. However, he’s still the most generous. Since 1999, Gates and his wife have helmed the Bill & Melinda Gates Foundation, one of the most powerful charities in the world. The foundation — which controls an endowment of more than US$40 billion — aims to lift millions of people out of poverty, with a heavy focus on eliminating HIV, malaria, and other infectious diseases. The couple is also working on a plan to bring mobile banking to the two billion adults who don’t have a bank account.

He’s also cofounder of the Giving Pledge, which he launched in 2010 with good friend and fellow billionaire Warren Buffett as a promise to donate 50% or more of their fortunes. The Giving Pledge now counts Mark Zuckerberg and Elon Musk among its members.

1. Jeff Bezos

Net worth: US$90.9 billion

Age: 53

Country: US

Industry: Technology

Source of wealth: Self-made; Amazon.com

He earned his massive fortune by introducing e-commerce to the world. After spending time on Wall Street, Bezos founded Amazon.com in the garage of his Seattle home in 1994 and operated it exclusively as an online book retailer. The company went public three years later and has since grown into an online behemoth, selling everything from furniture to food to Amazon’s own consumer-electronics products. The company has even got its claws into the grocery sector, making a US$13.7 billion bid for Whole Foods in June.

Bezos also has interests outside of Amazon, including investments in his privately owned space company Blue Origin, which successfully launched its first spacecraft in 2015, and The Washington Post, the newspaper he bought in 2013.