Shares of Amazon closed at their highest ever, breaking $800 a share on Thursday.

The commerce and technology company's stock closed at $804.70 — above $800 for the first time — after hitting an all-time intraday high of $805.89 earlier in the day.

The company announced on Thursday that Handmade, its artisinal marketplace and Etsy rival, would launch in Europe. Shares rose 1.9 percent for the day.

Amazon has seen its stock rise 19 percent this year, after reporting mixed results in its two quarterly reports. The company has not been without its challenges, after an investigation by ProPublica found this week that its algorithm hid favorable price and shipping combinations from some customers.

Amazon is a "terrific" company that's going to continue to become more dominant, Dan Niles, founding partner of AlphaOne Capital Partners, told CNBC's "Closing Bell." But there's still uncertainty around the company's subscription loyalty program, Prime, he said.

"The thing is, though, you're also paying a pretty high valuation for it," Niles said. "We still don't know what Prime is contributing or how much it's driving.

— CNBC's Gina Francolla contributed to this report.