A composite integrated semiconductor device. In one embodiment, an input surge/noise absorbing circuit absorbs surge from an input signal, an attenuating circuit attenuates the input signal, and an electrical signal converting circuit converts the input signal to an output signal. The input surge/noise absorbing circuit, the attenuating circuit, and the electrical signal converting circuit together form a unit, and a plurality of these units are arranged in parallel in one semiconductor substrate to form the composite integrated semiconductor device, resulting in a reduction in the number of discrete components mounted on a printed circuit board.