American investors are poised to snap up three companies listed on the London Stock Exchange for a combined value of more than £5bn, as flagging share prices leave British companies vulnerable to takeovers.

Alphawave, which is one of the few semiconductor companies listed in the UK, received an offer worth 183p a share from the US rival Qualcomm and on Monday the British company’s board recommended the deal to shareholders after months of talks.

The deal values the company, which designs and licenses high-speed connectivity technology that can be applied in datacentres and AI applications, at $2.4bn (£1.8bn).

Related: UK banks to experiment with Nvidia AI in ‘supercharged sandbox’ scheme

Its takeover is one of three deals that emerged on Monday, as the UK quantum computing startup Oxford Ionics agreed to a $1.1bn takeover by its US rival IonQ.

Oxford Ionics, which was spun out of the University of Oxford, was founded by the physicists Chris Ballance and Tom Harty in 2019. Both founders will remain at IonQ after the acquisition is completed.

IonQ, which is listed in New York, has a market value of $9.7bn, and its shares have more than quadrupled in value over the past year alone.

Meanwhile, shares in the precision and testing equipment specialist Spectris shot up by as much as 69% on Monday after it told its investors that it had received a takeover proposal from the US private equity company Advent.

The proposal, which the company said followed multiple earlier approaches from Advent, includes £37.35 a share and a proposed interim dividend of 28p a share, valuing it at £3.7bn. The jump in the share price pushed up its value to £3.4bn.

The board of Spectris, which is headquartered in London and operates in 36 countries, said it would be minded to recommend the takeover at that level if Advent makes an official offer. The private equity firm has until 5pm on 7 July to announce an offer or walk away, according to City rules.

The three deals are the latest in a string of high-profile companies in the UK that have been taken over by a bigger US rival or have switched their listing to New York in search for better liquidity and higher valuations.

The problem is particularly acute in the UK’s technology industry. While US markets have been dominated by tech players – including the “Magnificent Seven” group of companies – in recent years, the UK can boast just a handful of large listed companies in the sector.

Last week the online payments company Wise told investors it was planning to move its main share listing to the US. Deliveroo, the food delivery app, agreed to a £2.9bn takeover by its US rival DoorDash in May.