Apple could be most at risk of all the big American technology firms if the trade tensions between the U.S. and China escalate.

Late Monday, President Donald Trump threatened additional tariffs on $200 billion worth of Chinese goods. In response, China’s Commerce Ministry promised counter measures if Washington goes ahead.

It follows tariffs announced on Friday of 25 percent on up to $50 billion of Chinese goods, including semiconductors.

Investors will be watching how this impacts U.S. technology firms. Here’s what exposure they have to China.

“Apple is most exposed,” Neil Campling, co-head of global thematic group at Mirabaud Securities, told CNBC by phone Tuesday.

Drilling into the numbers you can see why. In its last fiscal year, Apple generated nearly 20 percent of its revenues from Greater China, which equated to $44.7 billion. In 2017, it shipped over 41 million iPhones into China and was the fifth-largest player in the market, according to data from IDC.

On top of that, it has around 40 stores in China. And it also operates its services such as the App Store and Apple Music in China. Services are an increasing part of Apple’s business as the smartphone market slows down; in the 2017 fiscal year, they accounted for 13 percent of total net sales, up from 11 percent in 2016. Apple does not break down how much of this came from China.

Apple also relies heavily on Asian suppliers. Its iPhones are assembled in China by Taiwanese firm Foxconn.

Arguably, Apple has become the most successful U.S. technology company in China but that same strength could be a vulnerability.

While Apple CEO Tim Cook reportedly got assurances from President Trump that iPhones assembled in China would not be subject to tariffs, there are still risk should a trade war escalate.

One risk is that Beijing clamps down on Apple’s suppliers, causing delays or even raising concerns about Apple products. The New York Times reported, citing a person close to the company, that this is a concern within Apple should the government do this under the guise of national security.

Authorities could also ban Apple services, which it has done before. In 2016, Apple’s iBooks Store and iTunes Movies were shut down in China.

Beijing could also push its own homegrown smartphone companies, like Xiaomi and Huawei. The latter faced scrutiny in the U.S. with intelligence officials cautioning U.S. consumers not to buy Huawei phones for fear of being spied on by the Chinese. China could theoretically adopt a similar message, saying the iPhone is a danger to national security.

Campling noticed that Apple’s inventories, which totaled $4.4 billion in the three months ending December 30, jumped to $7.6 billion in the March quarter. Inventories include completed products as well as components used in Apple devices. He said this was evidence that Apple was stockpiling components in case of any disruption and showed the company was concerned.

“It is a defensive/protective measure in case there are difficulties in future procurement or supply chain disruption as Apple is potentially in the crossfire of the U.S./Sino trade war,” Campling wrote in a note to clients Tuesday.

Among the other large technology firms, Google parent Alphabet is perhaps then next-most exposed.

Google makes the mobile operating system known as Android that is used in 77 percent of smartphones in China. While it is open source, Google makes money from the services it offers via Android such as cloud storage, YouTube or Gmail.

Should there be an escalation in trade tensions, it’s unclear whether Google may have to stop providing Android to smartphone makers in China, but it’s a risk to consider.

Google’s search engine has been blocked in China since 2010 and many of its other services are limited or unavailable. This means it derives very little revenue from China.

Similarly, other services-based companies including Facebook and Netflix have zero operations in the country. Facebook is blocked and Netflix has not expanded there. Amazon, as well, is dwarfed by online commerce giants JD.com and Alibaba. Amazon did launch its subscription Prime service in China in 2016, but it is a small market for the U.S. firm.

“We continue to strongly believe that, given the primarily services nature of traditional FANG names and very internationally distributed from a revenue perspective with China representing negligible revenue/growth, that Facebook, Amazon, Netflix, and Google/Alphabet are ‘primarily insulated’ from tariff worries and a potential retaliatory trade war with China if negotiations fail to result in a path to an agreement over the coming weeks,” Daniel Ives, head of technology research at GBH Insights, wrote in a note to clients Tuesday.

Chinese companies could definitely struggle. Huawei, the world’s biggest telecommunications equipment maker, relies on U.S. companies like Qualcomm and Intel for components for much of its hardware. It has already faced scrutiny in the U.S. and has been unable to fully enter the market.

ZTE is facing renewed issues after a defense bill passed by senate could effectively ban the company from buying components from U.S. firms.

Xiaomi, which is gearing up for the biggest initial public offering since Alibaba in 2014, makes smartphones and other devices like TVs. It has largely been focused on China and India, but a trade war could hamper its plans to expand over to the U.S., something executives at the firm have said is in the pipeline.

All of this could have the effect of making China look inward at its own technology scene and trying to boost homegrown semiconductor firms.

“China imports more semiconductors than they do oil so they are looking to internationalize production of semiconductors,” Campling told CNBC.

Already, Huawei has begun to create its own AI and 5G chips. And an increasing number of Chinese firms are likely to develop their own technology to reduce their reliance on America.