The formation and structure of glass is described and elementary wave-mechanics is used to show that, despite the disordered liquid-like configuration, electron energy-bands will nevertheless be formed in semiconducting glasses. The main effect of the disordered structure is to cause the formation of a high density of localized states in what would otherwise have been regions of forbidden energy. The localized states behave as traps for carriers and will have an important influence on the transport mechanisms in semiconducting glasses. The modes of transport are discussed and it is shown that, although a well defined energy gap does not exist, there is instead a ‘mobility gap’ which has a similar effect on electrical conduction.