The new iPhones are the iPhone 6S and 6S Plus, which have roughly the same overall dimensions as the last version.
"They look familiar, but we have changed everything about these iPhones," chief executive Tim Cook said.
One of the key new features is called "3D touch," which responds to pressure exerted on the screen to allow users to look farther inside messages and applications.
By responding to sensing pressure, the phones enable new "peek and pop" abilities to allow users dip in and out of content without losing their place. "Press lightly to peek at a photo, email, web page or other content, and press a little deeper to pop into the content itself," Apple said in a statement.
The new iPhones will use the upcoming iOS 9 operating system, which supports new features such as 3D touch.
Apple says that the main camera on the iPhone 6s and 6s Plus will have a resolution of 12 megapixels. It's the first increase since 2011, when the iPhone 4s got 8 megapixels, compared with 5 megapixels before. Meanwhile, the front camera for selfies is getting a boost to 5 megapixels, from 1.2 megapixels.
The 6S has the 4.7-inch (about 12-centimetre) display of its predecessor and the 6S Plus - one of the more popular handsets in the "phablet category" - has a 5.5-inch screen.
But the devices have more powerful processors that allow for improved graphics, harder glass and a new aluminum body, and keeps the same pricing as the earlier big-screen phones.