  Semiconducting transition metal dichalcogenides (STMDC) are two-dimensional
(2D) crystals characterized by electron volt size band gaps, spin-orbit
coupling (SOC), and d-orbital character of its valence and conduction bands. We
show that these materials carry unique exciton quasiparticles (electron-hole
bound states) with energy within the gap but which can ``collapse'' in the
strong coupling regime by merging into the band structure continuum. The
exciton collapse seems to be a generic effect in these 2D crystals.
