The iPhone grew as a platform in May to 43.5 percent of the U.S. smartphone market, encroaching on Android, which shrank slightly to 52.1 percent, according to comScore research data released on Monday.
In February, Android and iPhone accounted for a respective 52.8 and 41.7 percent shares, comScore remarked. Microsoft's Windows Phone fell from 3.5 to 3 percent by May, while BlackBerry slipped from 1.8 to 1.3 percent.
Apple notably retained the top spot in terms of individual smartphone vendors, beating out Samsung, which did at least advance a tenth of a percentage point to 28.7 percent. All other major vendors lost ground -- LG shrank from 8.3 to 8.2 percent, while Motorola dipped from 5.1 to 4.9 percent. HTC declined from 3.8 to 3.5 percent.
The iPhone has controlled a sizable portion of the U.S. market for years. Android gradually came to overshadow it as a platform, but mainly due to being cheaply and easily adopted by competitors, and some successful flagship products like those in the Samsung Galaxy S series.
Apple's positive performance versus Android in recent quarters has often been linked to the switch to bigger screens for the iPhone 6 and 6 Plus, which shipped in September 2014. Until then no iPhone had a screen bigger than 4 inches, even as some Android phones were approaching 5 or even 6 inches.
Two new iPhones, commonly known as the 6s and 6s Plus, could be announced as soon as next month. While retaining the same 4.7- and 5.5-inch sizes, they're expected to gain A9 processors, 2 gigabytes of RAM, and support for Apple Watch-style Force Touch controls.