In electronics, solid state circuits are those that do not contain vacuum tubes. The term was introduced to describe the transition from valve-based amplifiers to transistorised amplifiers. Solid state means that electrons flow through solid semiconductor, materials such as Germanium (Ge), Silicon (Si) etc, and not through empty spaces, such as in vacuum tubes. Solid-state components last much longer than their thermionic counterparts because of their greater resistance to shock, vibration and mechanical wear.

As the use of vacuum tubes in consumer electronics has decreased (an exception being the CRT still widely used for TV and desktop computer monitors), the term "solid state" has been increasingly used as a synonym for "no moving parts". For example, digital audio players that store all their songs in flash memory are often described as solid state to differentiate them from hard disk players. Like the older usage, this usage connotes increased durability and shock resistance.