The offer is the biggest for a foreign takeover of a UK technology firm and the largest ever Asian investment in the UK, telegraph.co.uk reports.
ARM designs the microchips that power smartphones and tablets, including Apples iPhone, and is at the forefront of developing low-power chips for the internet of things.
SoftBank promised to double jobs in the UK by 2021, that ARMs headquarters would remain in Cambridge, and that its management team would stay on.
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