Released in 1991, the Mega STE is a late-model STE mounted in the case of an Atari TT computer.

The 2 MB and 4 MB models shipped with a high-resolution mono monitor, and an internal SCSI hard disk[3] (the 1 MB model includes neither a monitor, hard disk nor hard disk controller).

While offering better ST compatibility than the TT, it also includes a number of TT features, from the ST-grey version of the TT case with a separate keyboard and system unit, optional FPU, a VMEbus slot, two extra RS232 ports (all 9-pin rather than 25-pin as previous models had), a LocalTalk/RS-422 port (no AppleTalk software was ever produced) and a 1.44 MB HD floppy support.

A unique feature of the MEGA STE in relation to previous Atari systems is the software-switchable CPU speed, which allows the CPU to operate at 16  MHz for faster processing or 8  MHz for better compatibility with old software.

An upgrade to the operating system was also produced after the first units were shipped that upgraded the onboard ROMs to TOS 2.05 and later to 2.6/2.06.