PURPOSE: To obtain a variable resistor with small patterns by a method wherein diffusion resistance is formed in a semiconductor of the first conductivity type by means of diffused wiring layers of the second conductivity type, and these wiring layers are designated as the source and drain of a FET for resistance control purpose.

CONSTITUTION: The variable resistor is composed of a ladder resistor consisting of diffused resistors 13, 14, and 15, a P-channel FET16, and a P-channel FET18. The FET16 has the source and drain formed by means of the resistors 13 and 14. The FET18 has the source and drain formed by means of the resistors 14 and 15. The resistance value of the variable resistor, i.e., the resistance value between terminals 11 and 12 is made variable by the potentials of gate terminals 18 and 19.