TOKYO—Sony Corp. said it would issue new shares for the first time since 1989, part of a $3.6 billion capital-raising plan that highlighted the potential of its fast-growing sensor business but left some investors nervous.

Sony’s stock closed 8.25% lower on the day at ¥3,461. Analysts cited the dilution of existing shares but said the decline could be short-lived given the consensus that Sony has turned a corner after years of losses.

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