Chinese customers visit an Apple Store in Hong Kong. Marcio Rodrigo Machado | S3studio | Getty Images

Technology companies including semiconductor giants and iPhone maker Apple have the most to lose from further U.S.-China trade tensions as world leaders gather at the Group of 20 summit later this month, according to Citigroup. Though Citi researchers' base case is that the two economic powerhouses will reach a "preliminary understanding" on trade at the Buenos Aires meeting, the analysts also expect President Donald Trump's administration to continue to impose more trade and investment restrictions on China. Specifically, Citi says it's likely the White House will crack down on certain U.S. exports, with an extreme scenario including a ban on sales of U.S. semiconductor components to China. That could have an outsized impact since China is one of the largest end markets for U.S. semiconductors, generating about 30 percent of total revenue for the industry. "The U.S. Department of Defense considers China a rising strategic competitor, and according to the U.S. Trade Representative, China has conducted industrial espionage and other market-distorting practices," Citi's Cesar Rojas and Catherine Mann wrote Tuesday. "The temporary impact on the semiconductor sector of a total ban on U.S. product to ship in to China would be devastating to the industry, as much of the largest end market products for semiconductors (PCs, cell phones, consumer electronics) are manufactured in China."

Such a decision could send shock waves across the sector, including San Diego's Qualcomm and Boise's Micro, which generate 65 percent and 57 percent of their revenue from China, respectively. Semiconductor capital equipment manufacturers — which build and sell machines used in electronic devices — could also take a hit. Rojas and Mann highlighted the negative impact trade restrictions have had at Ichor Holdings and Applied Materials, which have both lost nearly one-third of their market value in 2018. But additional trade barriers could also spell more trouble for the largest U.S. company, Apple. The iPhone maker's stock has rallied and retreated over the past year, tracking dovish and hawkish trade comments between Washington and Beijing. Apple's stock fell Tuesday, for instance, after Trump suggested he could place a 10 percent tariff on iPhones and laptops imported from China and said it's "highly unlikely" that he would delay an increase in tariffs to 25 percent from 10 percent on Jan. 1. Apple's products are currently exempt from the tariffs. It previously announced that the tariffs would affect the Apple Watch, AirPods and other products, but these were spared when the tariffs were announced. While iPhones are assembled in China, several parts required to make the smartphones are imported from the U.S.