To present a semiconductor device mounting ESD protective device appropriately applicable to transistors mutually different in dielectric strength, and its manufacturing method. The semiconductor device comprises a first ESD protective circuit 1A including a first transistor 3 and a first ballast resistance 4, and a second ESD protective circuit 1B including a second transistor 5 and a second ballast resistance 6. The impurity concentration of the second diffusion region forming the first ballast resistance 4 is set lower than the impurity concentration of the fourth diffusion region for forming the second ballast resistance 6.