According to Lange, Semi-metals are: boron, silicon, germanium, arsenic, antimony, tellurium, polonium and astatine. Although, polonium and astatine, according to some authors, are not semi-metals. Gallium is a metal (4. period, 13th (IIIa) group).
Astatine is not a good conductor of electricity. This is because it is a non-metal. All non-metals do not conduct electricity, and all metals do. The one exception is carbon, which is a non-metal, but conducts electricity well.
In 1940, astatine was produced in a lab at the University of California by the three scientists named Carson, Mackenzie, and Segre. This element is classified as a semi-metal and has the atomic number of 85.
Astatine, with the symbol At and the atomic number 85, is usually classified at a metalloid, but this is in dispute. It is sometimes classified as a halogen, and possibly a metal. It is still being studied.
Polonium and astatine may or may not be included as metalloids (depends on your periodic table). Overall, polonium is closer to being metal than a metalloid; astatine closer to being non-metal than metalloid