As shown in FIGS. 5 and 6, on an insulating substrate 10 is formed gate wiring 20, 21, 22 and 23 with a thickness of 1000 to 3500 ??? which is made of a conductive material such as aluminum or aluminum alloy, chrome or chrome alloy, molybdenum or molybdenum alloy, chrome nitride or molybdenum nitride, etc.