Why did transistors eventually replace valves in radios?

"Valve" is the British Word for Vacuum Tube, so for the British (which the person asking this question probably is) transistors did replace valves. Therefore the answer remains that values(vacuum tubes) where large and bulky, in addition they require high levels of power to function and created substantial heat and were quite fragile. The creation of the Transistor and then micro chip allowed for portability, lower levels of operation power to be required and reduced costs due to mass production