https://doi.org/10.1351/goldbook.S05597
Any transition from a semiconductor to a metallic state under the influence of a temperature or pressure change or both. Examples:
  1. Ti2O3: band-edge crossing in a semiconductor to semimetal transition.
  2. SmS: localized level crossing a band edge. In SmS hydrostatic pressure above the critical pressure Pc0.65 GPa broadens the Sm-5d band to make the band edge cross the Sm-4f6 level.
  3. A localized-itinerant transition.
  4. A switching transition.
Source:
PAC, 1994, 66, 577. (Definitions of terms relating to phase transitions of the solid state (IUPAC Recommendations 1994)) on page 590 [Terms] [Paper]