A trimmable resistor circuit and a method for operating the trimmable resistor circuit are provided. The trimmable resistor circuit includes first sources/drains and first gate structures alternatively arranged in a first row, second sources/drains and second gate structures alternatively arranged in a second row, third sources/drains and third gate structures alternatively arranged in a third row, first resistors disposed between the first row and the second row, and second resistors disposed between the second row and the third row. In the method for operating the trimmable resistor circuit, the first gate structures in the first row and the third gate structures in the third row are turned on. Then, the second gate structures in the second row are turned on/off according to a predetermined resistance value.