Prior to 1947, the invention of the world's first transistor, a big problem in communication technology was amplification, the received signals were extremely weak and could not produce a loud sound without being amplified. Another problem was the short comings with valves (unreliable, high power consumption, size and warm up time), therefore the need to replace valves were brought about, not only because of the limitations of vlaves but also because of the high demand for communication technology. Therefore research into the properties of semiconductors rose in attention.
Pretty much a remember it history dotpoint