Nvidia 'seems bubbly' because it won't be able to maintain its dominant market share, investing legend Rob Arnott says

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• Nvidia "seems bubbly" as its semiconductor market share isn't sustainable, Rob Arnott told CNBC.
• Competitors such as AMD and Intel will likely step up efforts to compete with the chip maker.
• Nvidia reported another big quarter of earnings Wednesday, beating both revenue and profit estimates. 

Nvidia has once again transcended Wall Street estimates, and its latest earnings beat has set off a chain reaction of price target increases.