Patent ID: 8093923

Claim:
A semiconductor device comprising: a first logic circuit region formed on a main surface of a first conductivity type semiconductor substrate, including a first resistance and a first logic circuit operating with a first driving voltage to control an operation of a predetermined switching element, and applied with a first voltage as a bias voltage; an annular region annularly formed on the main surface of said semiconductor substrate to circumferentially surround said first logic circuit region and including a field-effect transistor and a second resistance which are electrically connected to said first resistance; an isolation region formed between said first logic circuit region and said annular region, and providing electrical isolation between said first logic circuit region and said annular region; and a second logic circuit region formed on the main surface of said semiconductor substrate located outside said annular region, including a second logic circuit electrically connected to said field-effect transistor and said second resistance to operate with a second driving voltage, and applied with a second voltage as a bias voltage lower than said first voltage, said first logic circuit for controlling the operation of said switching element based on a predetermined potential difference caused by a drain current flowing through said first resistance when said field-effect transistor is turned on, said second logic circuit for detecting a current flowing through said second resistance to thereby determine a gate voltage to be applied to a gate of said field-effect transistor in order to cause a constant current to flow as said drain current, and apply said gate voltage to said gate, said annular region electrically isolating a drain of said field-effect transistor applied with said first voltage with respect to said second logic circuit region, and said isolation region electrically isolating said first logic circuit region at least by said first driving voltage with respect to the drain of said field-effect transistor which is applied with said first voltage.