emitter base resistance of the npn parasitic transistor 12 for simplification fig2 shows the junction of five drain contacts 9 to obtain a better effect however it is preferable to dispose 10 or more drain contacts 9 for example when this nmos transistor is used in an output circuit of an integrated circuit ic the gate electrode 6 is connected to an internal circuit of the integrated circuit and the drain electrode d is connected to the output terminal further the source electrode s and the backgate electrode bg are grounded in this nmos transistor when a positive electrostatic surge is applied to the output terminal an electric current flows toward the gate electrode 6 in the n type drain region 2 having the parasitic resistance component 13 this generates a potential difference v eb between the emitter and the base of the vpnp transistor 11 when this potential difference v eb between the emitter and the base is not less than a predetermined potential difference v e the vpnp transistor 11 is conducted as a result the npn parasitic transistor 12 is conducted causing a positive electrostatic surge applied to the output terminal to be escaped to the ground the potential difference v eb generated between the emitter and the base of the vpnp transistor 11 can be controlled by the resistance value of the parasitic resistance component 13 accordingly as far as this parasitic resistance component 13 has a suitable resistance value the vpnp transistor 11 can securely be conducted to prevent an.