Heres an emulator that emulates both the Sega Master System and the Sega Game Gear, heres the release notes:

MasterGear v4.1 for Windows is released. MasterGear is a program that emulates 8bit SEGA videogames on your computer. It runs games made for SEGA MasterSystem (Mark3 in Japan) and GameGear, as well as their predecessors: SG1000, SC3000, SF7000, and Mark2. MasterGear will also help hobbyists who still write software for these systems to debug their works without using rare and costly development hardware.

MasterGear v4.1 for Windows Changelog:
Greatly improved automatic hardware and language detection.
Fixed scanline length to 228 CPU clocks.
Made NTSC screen length to be exactly 262 scanlines.
Made PAL screen length to be exactly 313 scanlines.
Added multiple monitor support to MG-Windows.
Fixed disappearing window in MG-Windows.
Fixed best full-screen mode detection in MG-Windows.
Fixed window flicker that appeared after recent Win10 updates.
Fixed DirectInput joysticks support in MG-Windows.
Made directional pads work on XBox gamepads.
Switched MG-Linux to using PulseAudio sound.
Updated old PulseAudio driver for 64bit Linux.

download -->