The maximum concentration of impurity that can be dissolved in another material under equilibrium condition is called the solid solubility.

Portion of line, in phase diagram, representing solubility is called solvus curve.

Solid solubility of As in Si is large number and its means As can be used to form very heavily doped and therefore low resistance regions such as source and drain contacts for MOS transistors and emitter collector contacts in BJT.

For most of impurities in silicon, solid solubility increase with temperature, reach a peak value and fall down rapidly as melting point is approached. This is commonly referred as retrograde solid solubility characteristics.

Solid solubility of dopants exhibiting multiple charge state is a function of the Fermi level.