Newly public electric-vehicle maker Rivian Automotive is already trading at more than double Tesla 's lofty valuation, according to one analyst's unconventional valuation method. "I think Rivian's valuation is a full standard deviation outside of aggressive," Gene Munster, managing partner at Loup Ventures, told CNBC's "Squawk Box" on Thursday. Rivian shares are popping again on Thursday, up nearly 18%, after ending the day up 29% when they debuted Wednesday in one of the biggest IPOs of the year. The company, a start-up backed by Amazon and Ford , already has a market valuation larger than Ford and General Motors . Munster said he feels "uncomfortable" with Rivian's sky-high valuation, as compared with electric-car market leader Tesla. Rivian's "vehicles sell for an [average selling price] of $80,000. That's similar to Tesla's model S and X ... and those units on an annual basis have essentially topped out at 70,000 vehicles a year. If you apply a 70,000-vehicle delivery number for 2023 ... that means that the valuation per vehicle delivery in 2023 is $1.3 million. Tesla, excluding all of their energy business and insurance and other X factors, is valued in 2023 at about $500,000," said Munster. When you put Munster's valuation method together, Rivian is trading at about 2.5 times Tesla's valuation. "It does beg a question of why is this happening to Rivian's stock and can it continue," said Munster. Interest in Rivian could come from institutions' trust in the company's backers Amazon and Ford, he said. "One side is institutions were there from the beginning ... and the reason why they participated in Rivian versus these many other EV companies ... is institutional quality," Munster said. "That gives big companies like T. Rowe [Price] comfort that this in fact is going to be around for a long time."