Gallium arsenide is a gray solid. It makes crystals in a cube shape. It reacts slowly with water and quickly with acids to make arsine. It oxidizes in air.
Gallium arsenide is mainly used as a semiconductor. It has several things better about it than silicon. The semiconductors made are faster and higher power. LED's using gallium arsenide are efficient. Silicon, though is cheaper. Silicon dioxide is a good insulator; gallium arsenide does not make a good insulator like silicon does. Silicon semiconductors also take less power than gallium arsenide ones.