Japan's SoftBank Group reported Tuesday that net profit more than doubled in the second quarter thanks to a boom in AI-related share prices that has fuelled fears of a market bubble.

The tech investment giant -- a major backer of ChatGPT-maker OpenAI -- logged a net profit of 2.5 trillion yen ($16.2 billion) in July-September, up from 1.2 trillion yen in the same period last year.

SoftBank also announced it sold $5.8 billion worth of shares in US chip giant Nvidia last month, after the quarter had ended.

The group's earnings often swing dramatically because it invests heavily in tech start-ups and semiconductor firms, whose stocks are volatile.

In recent months optimism over the promise of AI technology has sparked a rush of multi-billion-dollar deals -- sending tech shares soaring wor

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