The online retailer did not release any specific sales figures for the OMAP 4-powered slate, nor did it clarify whether the bestseller tag applies to current sales or all-time figures.
The vague announcement is thought to be a warning shot to Apple, who is expected to enter the budget tablet market today with the launch of the so-called iPad Mini.
Amazon's Kindle Fire HD, available in 7-inch and 8.9-inch models, is the first tablet to support MIMO technology for improved Wi-Fi connectivity.
The device has two antennae on board for 41% faster connection speeds than Apple's third-generation iPad, and boasts an IPS display with a 1920x1200 resolution capable of hosting images in 254 ppi.
The 7-inch version of Kindle Fire HD is available to order in the UK at £159, and will ship in the territory on October 25.