Hermann Hauser said he was "very sad" at news of the £24bn ($32bn) takeover which was announced on Monday morning.
The Cambridge-based firm designs microchips used in most smartphones, including Apple's and Samsung's.
ARM, which was founded in 1990, employs more than 3,000 people.
Mr Hauser called ARM Holdings the proudest achievement of his lifetime.
'Real strength'
The man who helped spin ARM Holdings out from Acorn Computers in 1990 also said the technology firm had sold 15 billion microchips in 2015, which was more than US rival Intel had sold in its entire history.
Mr Hauser said ARM gave Britain "real strength".
He said it was a "British company that determined the next generation microprocessor architecture, that is going to be used in all the next generation phones and - more importantly - in the next generation of the internet of things".
ARM founder says Softbank deal is 'sad day' - BBC News
This is practically criminal negligence. ARM should have been seen as a strategic asset for the UK, much as Nokia was for Finland. How many high-tech design workers in Finland still work for Nokia. Why would anyone think the ARM design team is going to survive Japanese ownership.
$32bn is chicken feed for the company. It's only ten times what that dreadful Beats kit owner was given for his shoddy overpriced advert-driven headphones.
ARM lopped off
ARM lopped off
Nullius in verba ... ☎||||||||||| ... To Fate I sue, of other means bereft, the only refuge for the wretched left.
When flower power came along I stood for Human Rights, marched around for peace and freedom, had some nooky every night - we took it serious.
Who has a spare two minutes to play in this month's FG Trivia game! ... My other OS is Slackware.
When flower power came along I stood for Human Rights, marched around for peace and freedom, had some nooky every night - we took it serious.
Who has a spare two minutes to play in this month's FG Trivia game! ... My other OS is Slackware.
ARM lopped off
But they are expected to double the head count of employees in the UK and keep the primary design operations there.
ARM lopped off
You don't remember the wonderful Microsoft promises to Nokia?
Nullius in verba ... ☎||||||||||| ... To Fate I sue, of other means bereft, the only refuge for the wretched left.
When flower power came along I stood for Human Rights, marched around for peace and freedom, had some nooky every night - we took it serious.
Who has a spare two minutes to play in this month's FG Trivia game! ... My other OS is Slackware.
When flower power came along I stood for Human Rights, marched around for peace and freedom, had some nooky every night - we took it serious.
Who has a spare two minutes to play in this month's FG Trivia game! ... My other OS is Slackware.
ARM lopped off
I never believed Microsoft's promises to anyone.
ARM lopped off
Or theresa may's promises to look after british interests
Theresa May has been prime minister for five days – she just performed an about-turn on a £24bn takeover deal | Business News | News | The Independent
Last week, she said that the Government should be capable of stepping in when a foreign firm swoops for British businesses that are important to workers and communities. Today, Theresa May hailed the £24bn takeover of ARM Holdings by Japanese firm SoftBank
Theresa May has been prime minister for five days – she just performed an about-turn on a £24bn takeover deal | Business News | News | The Independent
Last week, she said that the Government should be capable of stepping in when a foreign firm swoops for British businesses that are important to workers and communities. Today, Theresa May hailed the £24bn takeover of ARM Holdings by Japanese firm SoftBank