Why semiconductors are opaque to visible light but transparent to infrared radiations?

Dear Student, Semiconductors can absorb ultraviolet and visible light for electronic transitions from valence band to conduction band and are hence, in general, opaque to ultraviolet and visible light. However, as they don't have free electrons in conduction band to absorb visible light and do intraband transitions within the conduction band. So, they are transparent to infrared. Regards