High voltage integration circuit with freewheeling diode embedded in transistor

A high voltage integrated circuit contains a freewheeling diode embedded in a transistor. It further includes a control block controlling a high voltage transistor and a power block-including the high voltage transistor-isolated from the control block by a device isolation region. The high voltage transistor includes a semiconductor substrate of a first conductivity type, a epitaxial layer of a second conductivity type on the semiconductor substrate, a buried layer of the second conductivity type between the semiconductor substrate and the epitaxial layer, a collector region of the second conductivity type on the buried layer, a base region of the first conductivity type on the epitaxial layer, and an emitter region of the second conductivity type formed in the base region. The power block further includes a deep impurity region of the first conductivity type near the collector region to form a PN junction.