The company said it would invest further in original TV content for Prime, which is to show the near motoring show headed by former Top Gear trio Jeremy Clarkson, Richard Hammond and James May later this year.
Founder Jeff Bezos also hailed the performance of Amazon's own devices such as the Fire TV Stick and the Echo voice-response system.
"We're building premium products at non-premium prices, and we're thrilled so many customers are responding to our approach," he said.