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).
They are actually called metalloid's. They are called such because their properties are between metals and nonmetal's in terms of physical properties and conductivity etc. A more technical definition...
Neither, it is a nonmetal
No. Semi-metals are their own class of elements.
A metalloid (semi-metal).
Boron is a metalloid or semi-metal