width w are 11 u03bcm 14 u03bcm and 80 u03bcm respectively also the values of the resistances of the resistors 4 39 and 5 are 1 2k u03c9 and 500 u03c9 respectively according to the invention a sufficiently high surge voltage protection effect is obtained for the following reasons i in the conventional device the contact 16 39 to the polycrystalline silicon through which the drain region 12 of the protective transistor 2 and the protective resistor 4 are connected to each other is extended over the entire length of the drain region in contrast according to the invention the opening 16 39 is reduced in size and formed at a location apart from the field oxide film 19 39 thereby preventing the concentration of electric currents at the defective part of the field oxide film ii the gate electrode 13 39 of the protective transistor 2 39 is connected to the ground voltage line 14 39 through a gate resistor 5 consisting of polysilicon thus facilitating the floating of the gate potential in the event of a surge voltage whereby the protective transistor 2 39 is easily turned on thus allowing the surge voltage to be relieved to the ground terminal iii the length l of the gate electrode 13 39 i e the channel region of the protective transistor 2 39 is made shorter at the central portion adjacent.