What are the difference between an ordinary switch and a semiconductor switch such as thyristor and transistor?

ordinary switch uses Mechanical means transistor switch controls electrical flow by the amount of current applied to the base of the transistor A thyristor is not really a switch. A thyristor is a four-layer semiconductor device, consisting of alternating P type and N type materials (PNPN). A thyristor usually has three electrodes: an anode, a cathode, and a gate (control electrode).