PURPOSE: To improve the accuracy of a resistance value of a diffused resistor layer which is formed by diffusing impurities into a semiconductor device even when an impurity concentration of the diffused resistor layer is lowered.

CONSTITUTION: A p-type resistor layer 2 is diffused using a resistor pattern from the surface side of an n-type semiconductor region 1. A p-type resistor surface layer 3 is very shallowly diffused on the surface of the resistor layer 2, using substantially the same resistor pattern, as that of the resistor layer, at a high impurity concentration. An insulation film 11 covers the surfaces of the semiconductor region 1, the resistor layer 2 and the resistor surface layer 3. Then, terminals 12 are led out of both ends of the resistor surface layer 3, whereby a diffused resistor 20 is obtained. The influence of accumulated electric charges caused by mobile ions in the insulation film 11 on a carrier distribution within the resistor layer 2 is interrupted by the resistor surface layer 3, whereby variations in resistance value of the diffused resistor 20 is reduced to less than ±0.1%, about one order of magnitude lower than with a conventional diffused resistor.