METHOD FOR MANUFACTURING SEMICONDUCTOR DEVICE AND ELECTRICAL APPLIANCE USING THE DEVICE

PROBLEM TO BE SOLVED: To provide a method for manufacturing a semiconductor device, in which, when a thick gate oxide film sufficient to secure a gate breakdown voltage of a high-voltage transistor is formed, the thick gate oxide film can be prevented from being reduced in thickness at the boundary between an element region and a trench isolation region, and a crystal defect caused by oxidation of a substrate material in a side wall portion of a trench isolation groove is prevented from being generated in an activation region of a low-voltage transistor having a small size.SOLUTION: A method for manufacturing a semiconductor device comprises: forming trench isolation regions 100c, 100f, and 100g on a surface of a semiconductor substrate 101 so as to isolate element regions each having a semiconductor element to be formed; thereafter forming silicon nitride films (oxidization prevention films) 109 so as to cover the trench isolation regions beyond the trench isolation regions to partially overlap the element regions in contact with the trench isolation regions; and then forming thermal oxide films 110 each having a thickness greater than that of a thermal oxide film required for the semiconductor element having a predetermined size out of the plurality of semiconductor elements.