Elon Musk has invested $50 million for Tesla Motors

Last Thursday, Tesla Motors Inc. Chief Executive Elon Musk has increased his investment in the electric-car maker, using more than $50 million of his own money to cover the taxes on shares that cost him less than $7 apiece.

Musk exercised and held 532,000 Tesla TSLA, +0.79% stock options this week, adding to his position in the electric-car maker, which amounted to 21.7% of the company as of August, according to FactSet.

According to an SEC filing detailing the transaction, Musk now owns slightly more than 28.9 million shares, which would be worth more than $5.5 billion at Friday’s closing price. Despite his already healthy investment in Tesla, Musk did not sell shares in order to pay the exercise price for the options nor for taxes, instead using his own cash, a Tesla statement explained.

Elon did not sell any shares even though he had to pay more than ($50 million) in taxes in connection with the exercise,” a Tesla spokesperson said in an email. Musk owned the right to exercise the options at their value on Dec. 4, 2009 — before Tesla went public. They were priced at $6.63, according to the SEC filing. That is less than 3.5% of the current going rate for Tesla shares, which closed Friday at $191.20.

 Tesla said Musk also used cash to pay the exercise price, which would have been slightly more than $3.5 million in total for stock worth more than $101 million. Musk is a major investor in Tesla as well as SolarCity Corp. SCTY, +0.08% , a solar-installation firm for which he serves as chairman, and he is also CEO and founder of SpaceX, a privately held space company valued at roughly $12 billion.

Musk increased his bet on SolarCity in 2015 amid some weakness for solar stocks, but his Tesla holdings are becoming a much larger portion of his personal portfolio. Tesla shares edged higher in late trading Friday after Musk’s investment was first reported.