We present a detailed study of GaSb-based monolithic vertical-cavity surface-emitting lasers (VCSELs) targeting an emission near 2.3 µm. These VCSELs rely on two n-type epitaxial semiconductor Bragg-mirrors and on a tunnel-junction for electron-hole conversion. Bragg mirror and active region designs, epitaxial material properties, device modelling, fabrication and performances are all addressed in order to fully assess the potential of this technology. Monolithic aperture-VCSELs, where carrier confinement is ensured by selective under-etching of the tunnel junction, have been fabricated in both bipolar-cascade VCSEL as well as single-stage VCSEL configurations. All devices have been thoroughly characterized and experimental data have been analysed in light of modelling trends. Our results give new insights into the physics of GaSb monolithic VCSELs and provide keys to their successful design. Further, they show that this technology is a viable option for tunable mid-infrared sources.