The invention describes a method for digitally calibrating a segmented current-steering DA-converter. In an embodiment of the present invention, the transistor comprises an amorphous oxide layer containing electron carrier at a concentration less than 1\xd710\u221218cm3, and the gate-insulating layer is comprised of a first layer being in contact with the amorphous oxide and a second layer different from the first layer. The body defines holes from the chip boxes to the outer surface of the body, said holes communicating with grooves formed along the outer surface of the body such that a continuous air passage is formed circumferentially around the body by each hole and respective groove.