q6 connected to the terminal 21 becomes lower than that on the base side of the parasitic transistor qs the npn parasitic transistor qs turns on in the first embodiment the p type substrate 1 is connected to the ground between the epitaxial layer 10 of the power transistors on the ground side and the epitaxial layers 11 of the power transistors on the power supply source side and the collector current of the npn parasitic transistor qs is mostly supplied by the epitaxial layers 11 of the power transistors on the power supply source side and the n type epitaxial layer 12 as a result the collector serial resistance res between the npn parasitic transistor qs and the small signal circuit portion 40 increases and therefore the parasitic current i cs flowing through the small signal circuit portion 40 decreases which prevents abnormal operations from occurring in the small signal circuit portion 40 as explained above the npn parasitic transistor qs draws the current mostly from the epitaxial layers 11 of the power transistors on the power supply source side and the epitaxial layer 12 of the n type island furthermore in the first embodiment there is an advantage that the power consumption by the current i c2 flowing through.